ABSTRACT 

Title of Thesis: THE EFFECT OF LANDSCAPE EVOLUTION ON THE 
VISIBILITY OF THE ARCHAEOLOGICAL RECORD: A CASE 
STUDY FROM DEEPLY BURIED SITE CA-SLO-16, MORRO 
BAY, CALIFORNIA 

Emily Marie Bales, Master in Professional Studies, 2023 

Thesis Directed By: Dr. Matthew Palus, Anthropology Department 

Morro Bay, California, is a biotically-diverse region with a rich cultural history.  In the archaeological 

community, there is an ongoing debate over the probable cause for an occupational hiatus in the region 

during the Middle Period (2600-1000 BP).  This case study addresses this disparity and presents the results 

of a single component, deeply buried, Middle Period archaeological site.  This thesis highlights how 

landform age, landscape evolution, and geoarchaeological methodology can affect the probability of 

identifying deeply buried archaeological sites.  Interdisciplinary data (e.g., seismology, geology, geography, 

paleoseismology) have proven useful in making a significant contribution in the understanding of a 

previously unknown period of occupation in Morro Bay.



THE EFFECT OF LANDSCAPE EVOLUTION ON THE VISIBILITY OF THE ARCHAEOLOGICAL 
RECORD: A CASE STUDY FROM DEEPLY BURIED SITE CA-SLO-16, MORRO BAY, CALIFORNIA 

by 

Emily Marie Bales 

Thesis submitted to the Faculty of the Graduate School of the 
University of Maryland, College Park, in partial fulfillment 

of the requirements for the degree of  
Master of Professional Studies 

2023 

Advisory Committee: 
Professor Matthew Palus, Chair 
Dr. Kathryn Lafrenz Samuels, Committee Member 
Dr. George N. Hambrecht, Committee Member 
Dr. Mary Margaret Furlong, Committee Member 
Ethan Bertrando, M.A., Committee Member 



© Copyright by  
Emily Marie Bales 

2023 



ii 

Dedication 

To my grandparents, without whom, none of this would have been possible. 



iii 
 

Acknowledgements 
 
 Countless friends, family, and colleagues deserve to be recognized here.  I am so lucky to have a 

community that has lifted me over the difficult times and celebrated alongside me during good times.  First, 

I would like to thank my brilliant professors at University of Maryland, College Park.  I would also like to 

thank my undergraduate professors and advisors, Jenn Perry, Mike Glassow, and Amber VanDerwarker.  

I am eternally grateful to the company in that I am lucky enough to be employed, Far Western 

Anthropological Research Group.  I cannot count the number of times my colleagues have listened to me 

talk about this research.  I thank Kathleen Montgomery and Jill Bradeen for the beautiful maps and figures 

used in this research.  A big thank you to Laura Harold and Jack Meyer for always answering my 

radiocarbon data questions, and to Jeff Rosenthal for providing books, finding references, and lending an 

ear when needed.  I would especially thank Phil Kaijankoski for his mentorship and advice throughout this 

whole journey.   

To my amazing peers in this program, especially Cody Haisley, Ken Gergely, and Bre Henderson.  

Solidarity!  To Bridget Wall who never wavered during my academic pursuit.  To fellow colleagues who 

encouraged me, John Berg, Mike Darcangelo, Kathy Davis, Annamarie Leon Guerrero (Mom), Chris Jazwa, 

Terry Joslin, Kristin Hoppa, Dusty McKenzie, Sarah Peelo, Jenn Perry, and countless more.  Wow, what a 

community to be in; I feel so lucky to be friends with brilliant, fun, kind humans.  I am truly surrounded by 

giants. 

 To my beloved friends, Ethan Bertrando, Lindsley Britton, Martijn Kuypers, Lauré Kwoka, Hughie 

Radde, and Kaya Wiggins who have made me laugh when I wanted to cry and light this paper on fire.  

Special shout out to Katie Hanrahan, Katie Metcalfe, and Ryan Phillip for everything. 

 To my amazing and hysterical husband, my talisman, Cameron Caywood.  I love you and I 

appreciate you.  Thanks for trekking up this mountain alongside me.  To my parents, the most reliable and 

strong people in my life.  And finally, to my grandparents, who would send me newspaper cutouts of 

archaeological digs around the world in the mail and whose encouragement never wavered. 

  



iv 
 

Table of Contents 

Dedication ..................................................................................................................................................... ii 
Acknowledgements ....................................................................................................................................... iii 
Table of Contents ......................................................................................................................................... iv 
List of Tables ................................................................................................................................................ vii 
Table of Figures .......................................................................................................................................... viii 
Chapter 1: Introduction .................................................................................................................................. 1 

1.1 Project Description .............................................................................................................................. 4 
1.2 Research Questions and Data Sources .............................................................................................. 5 
1.3 Thesis Organization ............................................................................................................................. 7 

Chapter 2: Theoretical Background .............................................................................................................. 8 
2.1 Geoarchaeological Approach .............................................................................................................. 8 

Geoarchaeological Assumptions ........................................................................................................... 9 
Soil Formation ........................................................................................................................................ 9 
Buried Site Sensitivity Model ............................................................................................................... 10 
Sensitivity Factors ................................................................................................................................ 13 

2.2 Seismological Approach .................................................................................................................... 13 
Fault Behavior ...................................................................................................................................... 14 
Wetland Development Model ............................................................................................................... 16 

2.3 Landscape Evolution ......................................................................................................................... 17 
2.4 Eustatic Sea Level, Relative Sea Level, and Submergence ............................................................. 19 
2.5 Temporal Component Definition ........................................................................................................ 20 
2.6 Application of Theoretical Framework ............................................................................................... 21 

Chapter 3: Morro Bay, California ................................................................................................................ 23 
3.1 Environment ...................................................................................................................................... 23 

Landform Age ...................................................................................................................................... 25 
Climate ................................................................................................................................................. 25 
Flora ..................................................................................................................................................... 26 
Marine Resources, Birds, and Terrestrial Mammals ........................................................................... 26 

3.2 Paleoenvironment .............................................................................................................................. 28 
3.3 Evolution of the Estuary..................................................................................................................... 29 

Chapter 4: Regional Cultural Context and Ethnography ............................................................................. 32 
4.1 The Central Coast Sequence ............................................................................................................ 32 

Millingstone Period (10,000-5500 cal BP) ........................................................................................... 33 
Early Period (5500-2500 cal BP) ......................................................................................................... 35 



v 
 

Middle Period (2500-1000 cal BP) ....................................................................................................... 36 
Middle-Late Transition (1000-700 cal BP) ........................................................................................... 38 
Late Period (700 cal BP – Historic Contact) ........................................................................................ 39 

4.2 Ethnography ...................................................................................................................................... 40 
Chumash .............................................................................................................................................. 41 
Salinan ................................................................................................................................................. 43 
Playaño ................................................................................................................................................ 45 

4.3 Past Archaeological Research at CA-SLO-16 .................................................................................. 45 
4.4 Geoarchaeological Testing at CA-SLO-16 ........................................................................................ 47 

Chapter 5:  Methodology ............................................................................................................................. 48 
5.1 Research Design ............................................................................................................................... 48 
5.2 Field Methods .................................................................................................................................... 49 

Cultural Resource Management Practices .......................................................................................... 49 
Project Components ............................................................................................................................ 49 
General Methods ................................................................................................................................. 51 
Stratigraphic Identification and Soil Descriptions ................................................................................ 51 

5.3 Phase II Testing Methods .................................................................................................................. 55 
5.4 Phase II Testing Results ................................................................................................................... 65 
5.5 Phase III Mitigation Methods ............................................................................................................. 65 

North Bridge Abutment ........................................................................................................................ 65 
South Bridge Abutment ........................................................................................................................ 66 

5.6 Laboratory Methods ........................................................................................................................... 66 
Chapter 6: Results ...................................................................................................................................... 68 

6.1 Phase III Data Recovery Results ...................................................................................................... 68 
North Bridge Abutment ........................................................................................................................ 68 

6.2 Special Studies .................................................................................................................................. 72 
Radiocarbon Dating ............................................................................................................................. 73 

6.3 Summary of Findings ......................................................................................................................... 73 
Chapter 7: Chronostratigraphy and Component Definition ......................................................................... 75 

7.1 Site Structure ..................................................................................................................................... 75 
North of the North Bridge Abutment .................................................................................................... 75 
North Bridge Abutment ........................................................................................................................ 76 
South Bridge Abutment ........................................................................................................................ 80 
Southern Pipeline Alignment ............................................................................................................... 80 
Stratigraphic Summary ........................................................................................................................ 82 

7.2 Temporal Indicators ........................................................................................................................... 82 
Radiocarbon Dating ............................................................................................................................. 82 



vi 
 

Temporally Diagnostic Artifacts ........................................................................................................... 83 
7.3 Component Definition ........................................................................................................................ 84 

Chapter 8: Middle Period Component Assemblages .................................................................................. 87 
8.1 Features ............................................................................................................................................ 87 

Feature 1 .............................................................................................................................................. 87 
Feature 2 .............................................................................................................................................. 87 
Feature 3 .............................................................................................................................................. 88 
Feature 4 .............................................................................................................................................. 88 
Feature 5 .............................................................................................................................................. 88 

8.2 Artifacts .............................................................................................................................................. 91 
8.3 Dietary Remains ................................................................................................................................ 92 

Chapter 9: Conclusion ............................................................................................................................... 100 
9.1 Research Questions and Goals ...................................................................................................... 100 

Middle Period Occupational Hiatus’ ................................................................................................... 100 
Landscape Evolution and Archaeological Methods ........................................................................... 102 
CA-SLO-16 and Morro Bay ................................................................................................................ 104 

9.2 Interpretations .................................................................................................................................. 107 
9.3 Future Research Opportunities ....................................................................................................... 108 

Research Potential from the CA-SLO-16 Excavations ...................................................................... 108 
Shellfish ......................................................................................................................................... 109 

Site Seasonality ............................................................................................................................ 109 

Fish Bone ...................................................................................................................................... 110 

Future Research Utilizing Landform Age, Landscape Evolution, and Geoarchaeological Methods . 111 
Appendix A: General Catalogue ............................................................................................................... 114 
Appendix B: General Field Methods ......................................................................................................... 122 
Appendix C: Laboratory Methods by Artifact Type ................................................................................... 125 
Bibliography .............................................................................................................................................. 130 
 

  



vii 
 

List of Tables 

Table 1: Central Coast Sequence ............................................................................................................... 33 
Table 2: Master Horizons ............................................................................................................................ 52 
Table 3: Subordinate Distinctions Within Master Horizons ......................................................................... 53 
Table 4: CA-SLO-16 Phase II and Phase III Excavation Summary ............................................................ 67 
Table 5: Radiocarbon Samples Collected from CA-SLO-16 ....................................................................... 72 
Table 6: General Summary of Cultural Materials from 2020 Geoarchaeological Testing at CA-SLO-16... 73 
Table 7: Summary of Mammal and Bird Bone Recovered from Phase II and Phase III Excavation at CA-

SLO-16 ........................................................................................................................................... 93 
Table 8: Summary of Fish Species from CA-SLO-16 ................................................................................. 95 
Table 9: Identified Fish Remains by Habitat Type at CA-SLO-16 .............................................................. 96 
Table 10: Shellfish by Habitat Type at CA-SLO-16 .................................................................................... 98 
 

 

  



viii 
 

Table of Figures 

Figure 1: Map of Morro Bay Region .............................................................................................................. 2 
Figure 2: Map of Project Location ................................................................................................................. 3 
Figure 3: Landform Age of Morro Bay Region ............................................................................................ 11 
Figure 4: Buried Site Sensitivity Map of Morro Bay Region ........................................................................ 12 
Figure 5: Plate Boundary Types ................................................................................................................. 15 
Figure 6: Relative Sea Level Map ............................................................................................................... 18 
Figure 7: Historic Map of Morro Bay ........................................................................................................... 24 
Figure 8: San Luis Obispo County Region .................................................................................................. 34 
Figure 9: Project Component Locations ...................................................................................................... 50 
Figure 10: North Bridge Abutment Stratigraphic Summary ........................................................................ 56 
Figure 11: North Bridge Abutment Soil Profile ............................................................................................ 57 
Figure 12: South Bridge Abutment Stratigraphic Summary ........................................................................ 58 
Figure 13: South Bridge Abutment Soil Profile ........................................................................................... 59 
Figure 14: Pipeline Alignment Excavation .................................................................................................. 60 
Figure 15: Slide-rail System in North Bridge Abutment .............................................................................. 61 
Figure 16: Slide-rail System in South Bridge Abutment .............................................................................. 62 
Figure 17: Phase II and Phase III Excavations of the North Bridge Abutment ........................................... 63 
Figure 18: Phase II and Phase III Excavations of the South Bridge Abutment .......................................... 64 
Figure 19: North Bridge Abutment Unit Location ........................................................................................ 69 
Figure 20: South Bridge Abutment Unit Locations ...................................................................................... 70 
Figure 21: Pipeline Alignment Soil Stratigraphy.......................................................................................... 71 
Figure 22: 2020 Geoarchaeological Core Locations .................................................................................. 77 
Figure 23: Cross Section Locations ............................................................................................................ 78 
Figure 24: Site CA-SLO-16 Soil Profile Schematic ..................................................................................... 79 
Figure 25: Morro Bay City Soil Profile Schematic ....................................................................................... 81 
Figure 26: Contracting-Stemmed Projectile Points ..................................................................................... 85 
Figure 27: Feature 1 .................................................................................................................................... 89 
Figure 28: Feature 2 .................................................................................................................................... 89 
Figure 29: Feature 3 .................................................................................................................................... 89 
Figure 30: Feature 4 .................................................................................................................................... 90 
Figure 31: Feature 5 .................................................................................................................................... 90 
  



1 

Chapter 1: Introduction 

Along the central coast lies one of the least known and last studied estuarine environments in 

California (Jones et al. 2019:1).  Morro Bay, a small seaside town in San Luis Obispo County, is an 

incredibly biotically-diverse and culturally rich region (Figure 1).  Archaeological research in the Morro Bay 

region has increased in the last thirty years, however studies have been isolated to either academic 

endeavors, which have been sparse (e.g., Joslin 2010; Phillip 2023; Wiggins 2022), or compliance work 

(e.g., Berg 2014; Far Western Anthropological Research Group 2016; Kaijankoski et al. 2019; Levulett and 

Fung 1993; Mikkelsen and Berg 2016; Mikkelsen et al. 1998;), which are often limited in both budget and 

time.  Geoarchaeological research has been even more restricted and intermittent to preconstruction 

archaeological testing to determine the presence or absence and depth of an intact cultural deposit.  Due 

to its methodology, (e.g., coring and mechanical trenching), geoarchaeological studies can offer 

archaeologists a chance to study cultural deposits that are deeper than safe hand-excavated testing allows.  

The research that has been conducted in Morro Bay has led to an ongoing debate within the discipline 

regarding a Middle Period occupational gap in Morro Bay’s chronology; whether it exists, and if it does, 

what caused it (Jones et al. 2019; Wiggins 2022).  This thesis will address the following questions:  

1. What explains the apparent Middle Period gaps, specifically the Late Middle Period gap, in Morro 

Bay’s archaeological record?  What human activities were happening during that time?   

2. How does landscape evolution and archaeological methodology affect the identification of deeply 

buried archaeological sites?   

3. How does site CA-SLO-16 fit into the larger context of Morro Bay’s prehistory and chronology? 

Jones et al. (2019:25) argue that the gap is due to possible seismic activity, noting an “abrupt 

habitat deterioration which made for an overall unstable environment,” specifically during the Middle Period.  

This theory is supported by Gallagher (1996:212), who states that between 2600-1400 cal BP “movements 

along the fault zone produced an abrupt deepening of the bay causing a sudden rise in relative sea level.”  

Jones et al. (2019:17) theorize that “an abrupt rise in sea level could have affected shellfish habitat within 

the estuary.”  Later in the volume, Jones et al. (2019:242) state the estuary may have been cut off from the  



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4 
 

ocean during this time, implying the water level either stayed at the same level becoming stagnant or went 

up due to creek input. 

The research included in this thesis will address the possible seismic activity using seismological 

principles of plate boundary types, information collected from a recent study of subduction in the area, and 

the data collected from a Middle Period site excavated in Morro Bay.  The site, CA-SLO-16, is a deeply 

buried archaeological deposit, much deeper than regular archaeological methods allow access to. This site 

provides insight into the occupational hiatus previously mentioned, a period of time that has eluded 

archaeological research in the area.  Additionally, available data produced by outside disciplines (e.g., 

seismology, geology, geography, paleoseismology) have been proven useful to better understand human 

occupation at that time (Gallagher 1996; Hanson et al. 1992; Lettis and Hall 1994).  Although understudied, 

these interdisciplinary data have the potential to make a significant contribution in the understanding of a 

previously unknown period of occupation in Morro Bay.   

1.1 Project Description 

This thesis is one study of a much larger compliance project contracted by the City of Morro Bay 

(City) for a new Water Reclamation Facility (Figure 2).  Federal funding for the project initiated compliance 

with Section 106 of the National Historic Preservation Act as well as State legal compliance through the 

California Environmental Quality Act (CEQA).  These regulations require federal and California public 

agencies to consider the adverse effects of projects to historic properties.  The City of Morro Bay contracted 

Far Western Anthropological Research Group (hereafter Far Western) to conduct the archaeological 

identification, evaluation, and mitigation efforts for the project which included investigations at site CA-SLO-

16, adjacent to Morro Creek.  A series of poorly documented archaeological investigations have been 

conducted at this precontact site since it was first identified in the late 1940s.  Far Western’s effort at the 

site included a geoarchaeological study in 2020, from which Far Western concluded that further testing was 

required after identifying a deeply buried archaeological deposit (Kaijankoski 2020).  This thesis will detail 

the results of the Phase II testing and Phase III data recovery conducted at CA-SLO-16 and how the findings 

fit into the larger context of Morro Bay’s prehistory and chronology. 



5 
 

1.2 Research Questions and Data Sources 

The research discussed in this thesis differs from previous studies in Morro Bay because it uses a 

multidisciplinary approach, applying seismological and geoarchaeological principles to data collected from 

CA-SLO-16. The following are three research questions I will address in this thesis.  I also include what 

expectations I have for each question.  

1. What explains the apparent Middle Period gap in Morro Bay’s archaeological record?  What human 

activities were happening during that time?  

Based on data collected from other sites in similar environments (i.e., Cayucos, San Simeon, Diablo 

Canyon, etc.), it would seem unlikely that human populations abandoned Morro Bay during this time.  Native 

people were very resourceful and adaptable, utilizing both marine and terrestrial resources.  To assume 

that Indigenous communities would migrate out of Morro Bay in response to “abrupt [marine] habitat 

deterioration,” is to limit the abilities of past peoples to adapt, depending on the level of the deterioration 

(Jones et al. 2019:25).  The adaptability of Indigenous peoples has been seen throughout the 

archaeological record across California.  Although not an exact comparison, Braje et al. (2017) discuss a 

similar behavior on Santa Rosa Island off the coast of California. The Island Chumash’s exploitation of 

shellfish resulted in the near depletion of local ecosystems.  The island has limited terrestrial resources 

compared to the mainland, so the over-exploitation of shellfish led to adjusting subsistence strategies from 

shellfish toward productive fisheries to sustain the high population.  

2. How does landscape evolution and archaeological methodology affect the identification of deeply 

buried archaeological sites? 

I anticipate that the location of Morro Creek paired with naturally deposited alluvium has resulted 

in deeply buried sites.  Relying on landscape evolution models, site sensitivity models, and historic 

information greatly assists in the identification of buried sites.  I will discuss the historic route of Morro Creek 

in greater detail in the following chapters, as historic maps indicate that historically the creek was not in its 

current location.  Therefore, the identification of other deeply buried sites along Morro Creek could be 



6 
 

missed if normal testing methods were implemented.  This also applies to CA-SLO-16; if Far Western had 

implemented normal methods, the deeply buried cultural deposit could have been missed. 

3. How does site CA-SLO-16 fit into the larger context of Morro Bay’s prehistory and chronology? 

CA-SLO-16 is unique because it is one of the only deeply buried sites identified in Morro Bay 

(approximately 2.4 meters below surface).  Similar to the expectations of the research question above, 

archaeological methods, especially those utilized for Cultural Resource Management (CRM) projects, do 

not normally reach that depth unless the project’s depth of impact requires it.  Therefore, CA-SLO-16 tells 

us that other sites are either not being identified yet or inadvertently excluded from archaeological site 

inventory due to the depths of project impacts and methodology applied to the project.  This is not to suggest 

that archaeologists should conduct unnecessary excavations to find these deeply buried sites, but 

geoarchaeological methods may be a less invasive, more productive method to identify these sites. 

Far Western started this research as a contracted project to conduct archaeological identification 

which included presence-absence subsurface testing, in this case geoarchaeological coring, for new 

infrastructure.  The project progressed to a Phase II assessment and based on the positive results, Far 

Western concluded that further data recovery was required.  The phases employed at CA-SLO-16 provide 

an accurate representation of how a Cultural Resource Management (CRM) project progresses, with the 

addition of geoarchaeological methods. 

To answer most research questions from an archaeological deposit it is vital to determine the age 

or age range of the cultural deposit.  Field archaeologists complete this by first identifying soil structure and 

then by sampling the stratigraphic contexts (e.g., radiocarbon assays from shell or charcoal).  Temporal 

components are critical when deciphering human change over time.  Temporal indicators, such as 

radiocarbon dates, obsidian hydration data, and temporally diagnostic artifacts assist in the identification of 

temporal components.  A comparison and analysis of subsistence change, settlement patterns, 

environmental change, and human behavior cannot be made without first defining temporal components of 

a site.  The data compiled and analyzed for this thesis uses component definition to identify human change 

and behavior over time.  



7 
 

1.3 Thesis Organization 

This thesis is organized into nine chapters.  The first chapter, Chapter 1, provides a brief project 

description and outlines the research questions explored in this thesis.  Chapter 1 also includes 

expectations and assumptions for each research question.  Chapter 2 details the theoretical framework and 

models that guided this research.  Chapter 2 includes geoarchaeological and seismological approaches, 

basic principles of landscape evolution, the significance of temporal component definition, and how relative 

sea level rise affected the Morro Bay estuary.  The environmental setting and regional context chapters 

(Chapters 3-4) discuss the Central Coast Chronology, ethnographic research, and past archaeological 

research conducted at CA-SLO-16. 

Chapter 5 provides a brief discussion of the project’s research design, followed by a detailed 

account of the field and laboratory methods utilized during both the testing and data recovery phases of 

this research.  Because this project was investigated throughout two phases, Chapter 5 includes very brief 

results of the testing phase (Phase II).  Chapter 6 details the results of the data recovery (Phase III) and a 

summary of findings.  Chapter 7 synthesizes the excavation results, discusses the site structure, and 

identifies the temporal indicators.  Chapter 7 also applies these data to the larger chronostratigraphic data 

of Morro Bay’s city soil profile.  Finally, Chapter 8 discusses the site constituents including features, artifacts, 

dietary remains, and site seasonality.  Chapter 9 reevaluates the research questions asked at the beginning 

of this thesis, provides interpretations of findings, and a discussion of future research potential.  Due to the 

sensitive nature of cultural resources, the maps and figures included in this thesis will only include the 

general location of archaeological sites.  



8 
 

Chapter 2: Theoretical Background 

The following chapter will briefly discuss a series of theoretical principles applied to this research, 

and how these approaches apply to site CA-SLO-16. The theoretical framework described below reflects 

the multidisciplinary approach of this research.  

2.1 Geoarchaeological Approach  

Historically, researchers have defined geoarchaeology as a subdiscipline of archaeology or 

subdiscipline of geology, but it is now more widely accepted that geoarchaeology is a separate discipline 

altogether.  Geoarchaeology studies archaeological problems using earth science methods including 

geology, geomorphology, geography, pedology, and hydrology (Butzer 1982:5; Rapp and Hill 2006:1; Scher 

2011:11).  One major contribution of geoarchaeological studies is to identify deeply buried archaeological 

sites.   

Archaeological discovery probability is dependent on three factors (Scher 2011).  The first is site 

distribution during the time of occupation.  Site distribution can be affected by both environmental conditions 

and human behavior.  The second factor is site preservation, as environmental and cultural factors can 

cause disturbance or complete elimination of ancient sites (Rapp and Hill 2006).  And lastly, the recognition 

of sites, which is how sites differ from their surroundings based on site characteristics including size or 

abundance of artifacts (Scher 2011:12; Schiffer 1988; Schiffer et al. 1978). 

The most crucial factor that affects site discoverability is an appropriate methodology.  There is a 

bias instilled into traditional archaeological methods of surface survey and subsurface hand-excavation that 

decreases the potential discovery of archaeological resources due to sediment deposition.  Some landforms 

may have had multiple deposition episodes since human occupation, depending on the landform age, type, 

or location.  Thus, a cultural deposit could be deeper than common archaeological hand excavation allows.  

A geoarchaeological assessment can increase the discovery probability of archaeological sites depending 

on the landform type and site type.  Therefore, every study should start with a visibility and landform 



9 
 

assessment (Refer to Figures 3 and 4 for application to the Morro Bay region) to decide on appropriate 

methods.   

Geoarchaeological Assumptions  

Geoarchaeological and geomorphic studies rely on general principles and assumptions regarding 

stratigraphy, landform age, and soil formation (refer to Figures 3 and 4 for Landform Age and Buried Site 

Sensitivity Maps).  These assumptions allow geoarchaeologists to evaluate landscape evolution, determine 

buried site potential, and interpret human-environment interaction. 

Two basic stratigraphic principles are common in geoarchaeology: superposition and 

uniformitarianism.  Uniformitarianism assumes that the current processes that are observed are the same 

processes that operated in the past, “although the extent and duration of these processes may have varied 

over time” (Rapp and Hill 1973; Scher 2011).  The Law of Superposition assumes that if a deposit remains 

undisturbed over time, the lower deposits within a profile will always be older than those stratigraphically 

above (Boggs 1995; Harris 1979).  These principles help geoarchaeologists understand the evolution of a 

deposit and the relationship between each layer or strata of sediment.   

Soil Formation 

Soil formation assumes that if a well-developed deposit, or a soil with distinct horizons (e.g., A-

horizon, B-horizon, etc.), is identified, then it is either older or had been stable longer than those with little 

to no horizon development (Birkeland 1974; Birkland et al. 1991; Ritter et al. 2002; Scher 2011:17).  Soil 

formation also notes that as humans occupy a landform for an extended time, the physical characteristics 

of that landform are more likely to exhibit archaeological evidence as a more well-developed soil horizon.  

Thus, paleosols are soils that exhibit a formerly stable land surface through soil features, including 

horizonation, pedogenic structures, root traces, etc. (Birkland et al. 1991).  Geoarchaeologists use 

paleosols to help “enable correlation across broad regions and help attain chronologic resolution” (Scher 

2011:18).   

Geoarchaeologists acknowledge that landforms with well-developed soils offer an environment 

available for human occupation for a longer period of time than those with weakly developed soils 



10 
 

(Rosenthal et al. 2004).  Therefore, in a stable landform, deposits of longer occupation will be more distinct 

within the soil profile than those of shorter occupation.  In contrast, the rapid deposition and landscape 

instability are displayed by a lack of soil formation and erosional unconformities (Rosenthal et al. 2004).  

While evidence of past human occupation (archaeological deposits) is subject to the same processes that 

affect preservation, distribution, and visibility, as geological deposits, it is the progression of landscape 

evolution “that ultimately determines whether archaeological remains will be buried, destroyed, or 

redeposited” (Bettis 1992:119; Kuehn 1993; Rosenthal et al. 2004:9; Waters 1992). 

Buried Site Sensitivity Model  

Studying past landscapes is essential for understanding how and why past people chose where to 

live and how they moved within the ancient environment.  The introduction of geomorphological studies 

within archaeology opened an entirely new avenue for understanding environmental change and the natural 

factors that alter the environment, including global warming, flooding, sea-level rise, etc. (Byrd et al. 2010).  

This change is especially evident in soil stratigraphy, presenting profound changes in a short amount of 

time.  These drastic changes resemble a shift in environmental settings, which is reflected in the available 

natural resources.   

Archaeologists apply the Archaeological Sensitivity Model (ASM) to prospective project areas to 

identify greater or lesser site potential areas.  The ASM is the most commonly used and most effective way 

to identify surface sites, but the ASM does not consider the age of the landforms to which the model is 

applied, therefore ignoring the potential for deeply buried sites.  A buried site model assumes that older 

landforms, meaning those developed prior to human colonization of North America, cannot contain buried 

archaeological deposits (Meyer 2020; Rosenthal and Meyer 2004).  Younger landforms, in comparison, 

have more potential for sediment deposition and therefore more potential for buried sites.  Thus, 

geoarchaeologists consider the depositional age of a landform when determining buried archaeological site 

potential.   

  



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OSOS

MORRO
BAY

Morro Creek

Little Morro Creek

Willow Camp Creek

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Stream 0 1,000 2,000
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Figure 3: Landform Age Map of Morro Bay Region

Basemap Imagery: ESRI World Imagery (Clarity) Landform Age (cal BP)
Water
Historical-Modern (<100 years)
Historical-Modern (Channel)
Recent Holocene (600-100)
Medieval Climatic Anomaly (1150-600)

Latest Holocene (2200-1150)
Early Holocene (11,700-8200)
Younger Dryas (12,900-11,700)
Terminal Pleistocene (25,000-12,900)
Older Pleistocene (2.56 my-25,000)
Pre-Quaternary (>2.56 my)

(Provided with permission from Far Western) 11



!

!

!

CAYUCOS

LOS
OSOS

MORRO
BAY

Morro Creek

Little Morro Creek

Willow Camp Creek

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0 1,000 2,000

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0 250 500
Meters

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Figure 4: Buried Site Sensitivity of Morro Bay Region

Basemap Imagery: ESRI World Imagery (Clarity) Buried Site Sensitivity
Highest
High
Moderate
Low
Lowest

(Provided with permission from Far Western) 12



13 
 

In CRM, archaeologists are limited when discussing the potential for buried sites to the depth of 

impact, or the maximum depth of a project.  The buried site model, when applied to a CRM project, hinges 

on three factors: (1) the attractiveness for occupation, including access to natural resources (e.g., water 

source), topography1, and protection from the elements (e.g., aspect); (2) the landform age, as discussed 

above; and (3) the depth of project impacts (Refer to Figure 3 and Figure 4 for application). The latter 

differentiates CRM projects from academic research; buried site identification within academia is often 

applied to answer a specific research question, whereas, in CRM, the buried site sensitivity model is 

necessary to complete archaeological identification efforts for a project with deep impacts. 

Sensitivity Factors  

Due to the geoarchaeological assumptions above, California’s lowland depositional landforms have 

geological potential to contain deeply buried sites because most were formed after precontact occupation 

in the region during the Holocene.  Comparably, upland landforms, which formed prior to documented 

human occupation in the region, have had less deposition events and therefore, a lower potential for deeply 

buried sites.  This does not apply to older landforms that have been capped with younger sediment.  

Additionally, geoarchaeologists must acknowledge that archaeological deposits are not randomly 

distributed within a landscape but occur in specific geoenvironmental settings and therefore assist in the 

determination of a buried site location (Foster et al. 2005:4; Hansen et al. 2004:5; Kaijankoski et al. 2019:33; 

Foster et al. 2005:4; Hansen et al. 2004:5; Pilgram 1987; Rosenthal and Meyer 2004).  

2.2 Seismological Approach  

Although seismology is a few disciplines away from archaeology, the movement of the earth can 

have significant effects on the landscape and therefore impacts the human-environment relationship.  Jones 

et al. (2019), cite seismic activity as the leading cause of the Late Middle Period hiatus in Morro Bay, noting 

“seismic activity in the bay area…shut the estuary off from the sea and caused sudden deterioration of 

shellfish habitat” (246), “…causing human populations to temporarily withdraw from the area” (251).  The 

 
1 Topography has implications for both high and low sensitivity. 



14 
 

authors continue, “movements along the fault zone produced an abrupt deepening of the bay causing a 

sudden rise in relative sea level” (17; Gallagher 1996:212).   

Gallagher’s 1996 dissertation is the most cited document when discussing the hiatus of occupation 

in Morro Bay during the Middle Period (Jones et al. 2019; Wiggins 2022).  Gallagher’s research provides a 

detailed analysis and explanation for the relative sea level (RSL) change in Morro Bay over the past 4220 

years (1996).  The author compares the sea level rise of San Francisco Bay and worldwide rates to that of 

Morro Bay, stating that Morro Bay is comparable prior to 2500 BP and after 1500 BP.  However, Morro Bay 

displays a faster rate of RSL rise (3.0 mm yr1) between 2500 and 1500 years BP, compared to global data 

(Gallagher 1996:211).  “Elsewhere, late Holocene rates of RSL rise were generally between 1.0 and 2.0 

mm yr1 with local differences dependent upon the glacioisostatic, hydroisostatic and tectonic history of each 

area,” (Gallagher 1996:210).  Gallagher concludes that hydroisostatic or tectonic subsidence of the shelf 

caused this rapid rate of RSL rise comparing Morro Bay to the Pacific Northwest Cascadia subduction zone 

(Gallagher 1996:212-213):  “Comparing the Morro Bay RSL curve with these ages, the steep portion of the 

curve, with the rise of 3.0 mm yr1, occurs between 2500 and 1500 years BP, approximately covering the 

period of known activity on the Los Osos Fault’’ (Gallagher 1996:212).  

Fault Behavior  

To analyze how the environment reacts to seismic activity, it is essential to understand the 

fundamentals of fault behavior.  The Earth’s outer crust is comprised of a series of tectonic plates that move 

on the asthenosphere (US Department of Commerce, National Oceanic and Atmospheric Administration 

2014).  A plate boundary is where two tectonic plates meet (Figure 5).  There are three major types of plate 

boundaries; each plate boundary reacts differently both during co-seismic and between inter-seismic 

earthquakes, therefore resulting in different effects to the surrounding environment.  A convergent plate 

boundary occurs when two plates collide, moving beneath one another causing subduction.  An example 

of this process is the Cascadia subduction zone in the Pacific Northwest.    

  



Gradual Uplift at Cascadia Coast

Gradual Uplift at Cascadia Coast

INTERSEISMIC

OceanM
antle

Crust LOCKED
North America Plate

COSEISMIC

RUPTURE

Tsunami Sudden Coastal Subsidence

Juan de Fuca Plate

Figure 5: Example of Cascadia Plate Boundary Behavior

(Provided with the permission of Far Western) 15



16 
 

The second boundary type is a divergent plate boundary, which occurs when two plates move away 

from each other.  The final plate boundary is called a transform plate boundary.  This type of boundary is 

caused when two plates rub against each other in a horizontal motion, versus the vertical, upheaval motion 

of a convergent plate.  The San Andreas Fault in California is an example of a transform plate boundary.  

Gallagher (1996:211) claims that Morro Bay is a fault-controlled basin, stating “Morro Bay is underlain by 

active traces of the Los Osos Fault zone, a series of south-west dipping reverse faults, and thus may be 

subject to localized tectonic subsidence.”  The differences of plate boundary types and their behavior will 

be a significant discussion within this thesis. 

Wetland Development Model  

Orson et al. (1985) state that when sedimentation rates cannot keep pace with sea-level rise (>2.5 

mm yr1) wetland landscapes cannot develop fully or at all.  The Wetland Development Model uses 

stratigraphy, vegetation, and a three-dimensional development created by “linking core logs into fence 

diagrams,” (Gallagher 1996:225).  It is important to identify if a wetland existed during this time, because a 

lack of wetland could indicate a decline in the health of the local ecosystem and have negative impacts to 

the human communities who rely on these resources.  Kaijankoski et al. (2019) note a decreased fish 

presence in archaeological deposits during the first half of the Middle Period (2600–1000 cal BP), which 

could signify increased siltation in the bay.  Jones et al. (1994) also suggest that the estuary may have 

been cut off from the ocean at this time, providing similar examples of siltation and human abandonment 

along the California coast (Gallegos 1987, 1992). 

Jones et al. argue that seismic activity and the relative sea level rise resulting from subsidence that 

followed “could have shut the estuary off from the sea and caused sudden deterioration of shellfish habitat” 

(2019:246).  Gallagher states that “sedimentation rates calculated from radiocarbon ages never reached 

this rate2…[i]t seemed likely that a narrow, fringing wetlands existed in the upper intertidal zone around the 

bay…during this time” (1996:213).  Gallagher concludes the wetland has not been even or continuous, 

 
2 Gallagher was stating that the rate of sedimentation needed to maintain an intertidal wetland would be 3.33 mm yr1 
while radiocarbon ages never reached that rate, then RSL rise was too fast for significant wetlands to form, therefore 
Gallagher concludes that a narrow, fringing wetlands existed during the disputed time (1996:213). 



17 
 

which has resulted in “vertical and lateral progradation at irregular and discontinuous rates, so ages of 

sediments equidistant from the apex may be different” (1996:233).  Therefore, a single three-dimensional 

transect of the bay could not be assigned a reliable timeframe (Gallagher 1996:233).  Overall, it can be 

deduced that although a reliable timeframe could not be assigned to the bay, the wetland development 

model suggests that the waterline boundary of the bay may have provided plant resources during a time of 

previously hypothesized marine depletion.  Additionally, if an ephemeral wetland did exist, this could have 

also been true for the shellfish population. 

2.3 Landscape Evolution  

 Landscape evolution occurs across the landscape but most notable for this research, near 

waterways, creeks, rivers, and the coastline.  The route, amount of time, and result of introduced or 

increased water in an area all depends on the underlying geologic materials, but in general, water can 

move, deposit, and rearrange sediment across a landscape (Beckinsale and Chorley 1968; Davis 1889). 

Features of landforms are the result of continued change through erosion (i.e., wind, water, ice, etc.), which 

can create a cycle of erosion (Beckinsale and Chorley 1968).  Although this is a basic principle of the 

erosional cycle discussion within geomorphology, it directly applies to the research area. 

 Many of the modern geomorphological principles evolved from theories expressed by Davis in 

1889.  Coulthard and Van De Wiel (2012) explore the modeling of river history and evolution using some 

of the basic principles introduced by Davis.  The text includes brief explanations of landscape evolution 

models, alluvial architecture models, and meander models (Coulthard and Van De Wiel 2012:2123).  

Landscape Evolution Models, or LEMs, were introduced to study river networks and their evolution over 

time (Coulthard and Van De Wiel 2012:2126).  Alluvial Architecture Models (AAM) are often designed to 

“simulate the vertical and horizontal development of basin stratigraphy” (Coulthard and Van De Wiel 

2012:2129).  Both models have the potential to help archaeologists understand the depositional process of 

sediment over time.  Although some geologists use this information to understand the future structure of 

river landscapes and other waterways, archaeologists could apply the same principles to acknowledge 

floodplain evolution, and how a river or creek’s location may change over time, altering the landscape and     



!
Ol

d C
ree

k

San

Bern
ard

o Cre
ek

CA-SLO-16

Los Osos Creek

Morro Creek

Los Osos Creek

Toro Creek

Chorro Creek

Los
Osos Cree

k

Little Morro Creek

O! CA-SLO-16
Sea Level (meters below mean sea level)

1150 cal BP (-0.6 m)
2200 cal BP (-2.4 m)
4200 cal BP (-5.3 m)
6200 cal BP (-9.4 m)

8200 cal BP (-17.2 m)
9950 cal BP (-29.6 m)
11700 cal BP (-47.8 m)
12900 cal BP (-60.1 m)
14600 cal BP (-77.6 m) 0 1 2

Miles

0 1 2
Kilometers

Figure 6: Sea Level Rise Map of Morro Bay Region

(Provided with permission from Far Western) 18



19 
 

burying archaeological sites.  The research discussed in this thesis will not include the use of landscape 

evolution models, however it is imperative to understand landscape evolution and its effects on buried 

sites. 

2.4 Eustatic Sea Level, Relative Sea Level, and Submergence 

Before discussing the effects of sea level rise, it is important to understand the differences between 

relative sea level rise (depicted in Figure 6) and eustatic sea level rise.  Sea level can increase or decrease 

in several ways, including “variation in masses or volume in the oceans, or by changes of the land with 

respect to the sea surface” (Rovere et al. 2016:221).  Although it may seem incorrect, depending on the 

local events, relative sea level could increase while eustatic sea level decrease (Rovere et al. 2016). 

Eustatic Sea Level (ESL) is calculated by the distance from the center of the earth to the sea 

surface (Rovere et al. 2016; Schlager 2005).  The purpose of eustatic sea level reconstruction is usually 

applied to calculate how climate change related events (e.g., glacio-eustasy, thermical expansion, thermo-

steric changes, and halo-steric changes) affect global sea level.  Eustatic sea level can also be affected by 

geological forces that expand or minimize the volume of the ocean basins including tectonic seafloor 

spreading (tectono-eustasy) or sedimentation (sedimento-eustasy; Rovere et al. 2016:222).  

Relative Sea Level (RSL) change is isolated to a land-based reference frame (Kemp 2015).  Rovere 

et al. (2016) state, “land uplift or subsidence can result in…a fall or rise in sea level that cannot be 

considered eustatic as the volume or mass of water does not change” (222).  Relative sea level change 

can occur over a large spatial and temporal scale (Kahn et al. 2015).  A few of these causes include 

sediment compaction, tectonic deformation, or human activity (e.g., anthropogenic deposition, urban 

development; Ericson 2006).  Tectonic uplift and subsidence have been documented to be one of the 

primary causes of changes in relative sea level over short periods of time (e.g., the last century) and longer 

time scales (e.g., the Holocene or Quaternary; Dura et al. 2016; Kelsey and Bockheim 1994; Larson et al. 

2003; Kato 1983; Rovere et al. 2016:225; Shennan et al. 1996; Simms et al. 2016a; Vacchi et al. 2012). 

The Holocene evolution of the Morro Bay coastline near site CA-SLO-16 is depicted in Figure 6.  

This figure was developed using a model first introduced by Meyer et al. (2013).  The model creates a 



20 
 

three-dimensional landscape below the estuary and adjacent coast by using a combination of water depth, 

or bathymetry, and the sea floor topography.  To easily identify change over time, the lines on Figure 6 

correlate with a significant landmark in time (e.g., 11,700 cal BP correlates to the Younger Dryas).     

Simms et al. (2016b) conducted a study comparing estuaries developed in subsiding geological 

structures by looking at rates of vertical motion, relative sea level, and radiocarbon ages acquired from the 

gastropod Cerithidea californica shells from core samples. The core sample applied to this research was 

collected by Gallagher (1996) and interpreted by Simms et al. (2016b).  Compared to other nearby 

estuaries, such as Goleta Slough, Carpinteria Slough, and Campus Lagoon, Morro Bay experienced a 

higher rate of subsidence3 (Simms et al. 2016b).  Simms et al. argue that although Morro Bay’s bay was 

formed within a structural basin similar to other estuaries, the finger-like sandspit created a barrier between 

the bay and the ocean therefore “enhancing accommodation” (2016:1573).  All these factors contribute to 

the estuary and bay’s current location, size, and biotic and abiotic structure (Figure 6). 

A basic understanding of relative sea level change can open a range of research questions 

regarding subsistence based on environmental status.  Due to the native population’s apparent dependence 

on the estuarian and bay shellfish species, many researchers have alluded to regional migration in 

response to shellfish depletion.  This depletion was attributed to either the sudden deepening of the bay 

due to seismic activity (Gallagher 1996) or seismic activity that “shut the estuary off from the sea and caused 

sudden deterioration of [the] shellfish habitat” (Jones et al. 2019).  Relative sea level and subsidence will 

be discussed at length throughout this thesis. 

2.5 Temporal Component Definition 

Defining a site’s temporal component is the most important task in identifying change in human 

behavior over time.  Temporal components are identified by examining the horizontal and vertical site 

structure, analyzing temporally diagnostic artifacts, and adjusting methods to properly test, analyze, and 

document each component (Mikkelsen et al. 2013).  Temporal components are defined as “temporally 

related aggregates of artifacts, features, and other residues, representing the material remains produced 

 
3  For more information on how to calculate the rate of subsidence refer to Simms et al. 2016b. 



21 
 

during a specific time span of residence or other use at a specific location, and found associated with a 

definable horizontal/vertical fraction of a site or landform” (Mikkelsen et al. 2013: n.p.; White and 

Fredrickson 2002).   

After components are clearly identified within a site, archaeologists should only use component-

associated data for analysis.  Mikkelsen et al. (2013) argues that if an archaeologist does not identify 

temporal components, then research issues cannot be adequately addressed due to the lack of 

comparative data.  This argument applies to culture history, subsistence change, settlement patterns, trade, 

the human-environment relationship, exchange, and all other aspects of human behavior.   

2.6 Application of Theoretical Framework 

The theoretical framework outlined above will be applied as principles in which to analyze and 

discuss the research in this thesis.  Geoarchaeological framework will be applied to both the identification 

of site CA-SLO-16 and in the discussion of future identification of deeply buried sites.  Seismological 

principles provide significant insight to the interworking of plate boundary behaviors, which prove valuable 

when exploring the condition of the estuary and bay during the Late-Middle Period.  Additionally, the wetland 

development model suggests that the waterline boundary of the bay may have supported an ephemeral 

wetland during a time of previously hypothesized marine depletion.   

Landscape evolution is the common thread throughout this research.  Landscape evolution plays 

a significant role in the location of deeply buried archaeological sites and what methodologies should be 

implemented when testing for deeply buried archaeological sites.  Relative sea level and subsidence are 

discussed to provide a foundational knowledge of how a “sudden deepening of the bay” would occur 

(Gallagher 1996) and how this event may not have been dramatic enough to cause shellfish depletion.  

Finally, one of the most important discussions of this research, is the importance of temporal component 

definition.  As stated above, if temporal components are not defined then there is no comparative data to 

highlight change in human behavior and activities over time.  The case study discussed in this thesis 

highlights how an understanding of landscape evolution paired with geoarchaeological methodology can 

reveal deeply buried archaeological sites.  Additionally, the archaeological deposit identified, site CA-SLO-



22 
 

16, provided valuable insight into human behavior during the apparent Middle Period gap in Morro Bay’s 

chronology. 

  



23 
 

Chapter 3: Morro Bay, California  

As briefly discussed in Chapter 1, Morro Bay is a resource-rich coastal environment.  The estuary 

provides an environment able to house a diverse population of shellfish, fish, marine and terrestrial animals, 

in addition to plant resources.  As Morro Bay’s environment changes with relative sea level, seismic activity, 

and climate, the surrounding resources fluctuate creating an evolving ecosystem.  It is the mutability of 

Morro Bay’s environment that speaks to the resilience and adaptability of past occupants.   

3.1 Environment  

Morro Bay, located on the Central Coast of California, is one of California’s least-known and last-

studied estuarine environments (Jones et al. 2019:1).  Morro Bay region has a variety of biotic zones 

including grasslands, woodlands, and coastal sand dunes, creating a diverse biotic environment.  One of 

Morro Bay’s most notable features, the estuary and neighboring bay, is separated from the ocean by a five 

kilometer long, finger-like dune that is referred to as the “sandspit” (Figure 2).  Previously, the estuary was 

fed by three drainages, Chorro, Los Osos, and Morro Creek, but Morro Creek was diverted and now feeds 

directly into the ocean (Figure 7; Jones et al. 2019:8).  Morro Bay has been identified for hundreds of years 

by seafarers and travelers alike by its most significant landmark, Morro Rock.  Morro Rock is one of nine 

volcanic plugs in San Luis Obispo County dating back to the Oligocene; today, it is connected to the 

coastline by a man-made landform. 

It is important to acknowledge the environmental components of Morro Bay because of its diversity.  

Morro Bay is not only an estuary but has countless terrestrial resources as well; past Indigenous 

communities relied on both environments.  The following sections briefly describe Morro Bay’s diverse 

environment including geological and topographical setting, climate, flora, and fauna.  This section is 

followed by a summary of the paleoenvironment and evolution of the estuary.  This chapter will detail the 

diverse marine and terrestrial resources of Morro Bay, specifically in the research area.  Additionally, I will 

discuss environmental change over time and the resulting occupant adaptability.   

  



!

!

!

!

Sperm Lake

Historic Route of
Morro Creek

CA-SLO-16

CA-SLO-165

CA-SLO-2222

CA-SLO-2124

! Site Location
Morro Creek (Current)

O

0 200 400
Meters

0 1,000 2,000
Feet

Figure 7: Historic Map of Morro Bay shown with the USCS 1883 T-Sheet T-1662 

(Provided with permission from Far Western) 24



25 
 

Landform Age 

 Morro Bay is comprised of a variety of landforms that date from the pre-Quaternary (>2.5 million 

years) to the Recent Holocene (600-100 cal BP; Figure 3).  The age of surface landforms determines the 

potential for deeply buried sites due to depositional patterns.  Most lowland depositional landforms have 

the geologic potential to contain buried sites.  This is due to their formation during the Holocene as sediment 

was deposited while or after human occupation took place.  This does not mean archaeological sites do 

not occur on upland pre-Holocene landforms, but rather sites on these ancient landforms usually occur on 

the surface.   

Based on Figure 3, the eastern and southern portions of the immediate research area have a low 

or very low sensitivity for deeply buried sites due to the landform’s age (e.g., pre-Quaternary, Older 

Pleistocene, Terminal Pleistocene, etc.).  Comparatively, the west and northern areas of the research area 

contain landforms dating to the Recent Holocene (600-100 cal BP) and Medieval Climatic Anomaly (1150-

600 cal BP).  When preparing a buried site sensitivity assessment (Figure 4), certain geo-environmental 

settings must be taken into consideration in addition to landform age.  These geo-environmental settings 

include low, level landforms and proximity to present or past water sources (Foster et al. 2005:4; Hansen 

et al. 2004:5; Pilgram 1987; Rosenthal and Meyer 2004). 

Proximity to water is a consideration taken when applying the Archaeological Sensitivity Model, as 

water is a necessity for human existence.  In terms of the buried site sensitivity assessment, an active 

waterway, such as a river or creek, is also a sediment source.  As a creek ebbs and flows, meanders, 

widens and narrows throughout the seasons and over the years and as an effect of climate change, 

sediment is deposited causing sites to be buried.  This is also represented in Figure 3, as Morro Creek 

shows the landform age as Recent Holocene Alluvium. 

Climate 

The Central Coast of California has a very temperate, Mediterranean climate.  Although the 

summer months are warm and dry, coastal fog is not uncommon throughout the year.  The fog that blankets 

the immediate coastline provides moisture to plants and cools down the coast (Joslin 2010).  The warm 



26 
 

temperatures commonly extend into the fall months, while the winter months are cooler with most 

precipitation occurring between the months of December and March.  The unique Mediterranean climate 

allows for a variety of vegetation to thrive.   

Flora 

 Morro Bay’s estuarine landscape allows for several biotic zones within the terrestrial and marine 

environment.  The coastal sagebrush zone houses salt-tolerant taxa, including nightshade (Solanum spp.), 

verbena (Verbena lasiostachys.), coyote brush (Baccharis pilularis), beach bur (Ambrossia chamissionis), 

sagebrush (Artemesia californica), and saltbush (Atriplex spp.; Jones et al. 2019:9; Timbrook 2007).  In the 

near-shore scrub zone, bush lupine (Lupinus spp.) and deer weed (Lotus scoparius) can be found.  Morro 

Bay’s grasslands have replaced bunch grasses (Festuca idahoensis) and needle grass (Nasella spp.) with 

wild oats (Avena spp.), California poppy (Eschscholzia californica), native foxtail barley (Hordeum jubatum), 

and lupine (Lupinus spp.; Hickman 1993).  Chaparral species are also present including scrub oak (Quercus 

berberidifolia), fiddleneck (Amsinckia menziesii), and toyon (Heteromeles arbutifolia).  The woodlands 

include coast live oak (Quercus agrifolia), Monterey pine (Pinus radiata), and knobcone pine (Pinus 

attenuata; Jones et al. 2019).  The riparian zones, surrounding creeks and drainages, hosts an array of 

species, including oaks (Quercus spp.), elderberry (Sambucus spp.), bay (Umbellularia californica), 

blackberry (Rubus ursinus), and poison oak (Toxicodendron diversilobum; Timbrook 2007).  Jones et al. 

note that sedges (Carex spp), cattails (Typha spp.), and tule (Schoenoplectus spp.) were significant to 

native communities for weaving baskets and balsa rafts.  The plants described, and many more, were of 

great importance to Indigenous communities, therefore it is no surprise that many of these species can be 

identified in the archaeological record. 

Marine Resources, Birds, and Terrestrial Mammals 

 The marine environment is home to many species of fish and shellfish.  The open sandy beaches 

house Pismo clam (Tivela stultorum), razor clams (Siliqua patula), and olive shells (Callianix spp. previously 

referred to as Olivella biblicata) in the more protected areas.  Archaeological findings (Bertrando 2004b; 

Jones et al. 2019; Mikkelsen et al. 2000) have also alluded to native oysters (Ostrea lurida) being in 



27 
 

abundance in the past.  While California mussel (Mytilus californianus), abalone (Haliotis spp.), limpets 

(Lottia spp.), black tegula (Tegula funebralis), and barnacle (Balanus spp.) attach to intertidal rocks.  

California mussel (Mytilus californianus) is one of the most common shellfish types identified in 

archaeological assemblages in the Morro Bay region.  In the estuarine mud, over fifteen distinct types of 

clams can be found (e.g., Saxidomus nuttalli, Clinocardium nuttalii, etc.).   

Some schooling fish can be found in multiple environments throughout the year (e.g., sardines are 

found nearshore and open oceans, but spawn inshore).  While other fish species migrate to the estuary for 

spawning and feeding, including sculpin (Leptocottus armatus), surfperch (Hyperprosopon argenteum), 

flatfish (Pleuronectiformes), flounder (Platichthys stellatus), bat ray (Myliobatis californica), and requiem 

shark (Carcharhinus spp.).  A wide variety of fish species including rockfish (Sebastes spp.), staghorn 

sculpin (Leptocottus armatus), black perch (Embiotoca jacksoni), shiner perch (Cymatogaster aggregate), 

and lingcod (Ophiodon elongatus) prefer the rocky coast.  Fish that prefer the estuary and bay include 

shovelnose guitarfish (Rhinobatus productus), thornback guitarfish (Platyrhinoides triseriata), jacksmelt 

(Atherinopsis californiensis), and topsmelt (Atherinopsis affinis). Fish species found in freshwater resources 

include steelhead4 (Oncorhynchus mykiss) and threespine stickleback (Gasterosteus aculeatus).   

 Common marine mammals include sea otters (Enhydra lutris), harbor seals (Phoca vitalina) and 

sea lions (Zalophus californicus). Although archaeological data collected from Diablo Canyon, 

approximately 12 miles from the research area, indicates that elephant seals (Mirounga angustirostris) and 

northern fur seals (Callorhinus ursinus) were also present historically (Jones et al. 2019:10).  The coastline 

and estuary also attract over 75 bird species including waterfowl, shorebirds, and birds of prey (Gerdes and 

Browning 1974).  A few species include the great blue heron (Ardea herodias), snowy plover (Charadrius 

nivosus), and red-tailed hawk (Buteo jamaicensis). 

 Gerdes and Browning (1974) provide valuable information of the many native terrestrial mammals 

of Morro Bay and the environment in which they live.  Grassland and woodland environments have 

burrowing animals such as rabbits (Sylvilagus spp.), jackrabbits (Lepus californicus), squirrels 

 
4 Steelhead are technically anadromous. 



28 
 

(Otospermophilus beecheyi), and gophers (Thomomys bottae; Gerdes and Browning 1974:G-1).  Deer 

(Odocoileus hemionus) are also common in these areas, as well as tule elk (Cervus elaphus nannodes) 

historically (Mikkelsen et al. 2000).  Larger game identified within Morro Bay include brown bears (Ursus 

horribilis), bobcats (Lynx rufus), mountain lions (Felis concolor), and coyote (Canis latrans). These animals 

have also been identified in unlikely environments including near the bay and among the coastal dunes. 

3.2 Paleoenvironment   

 Paleoenvironmental models rely on pollen data from across California to infer on the climatic 

conditions of the Late Pleistocene.  West (2000) records cooler temperatures with a longer rainy season 

on the coast than the present based on pollen samples from the area.  Jones et al. (2019), provide a 

paleoenvironmental study using paleo-sea surface temperatures, climate, and relative sea level rise.  While 

stratigraphic and radiocarbon samples suggest that glacial recession was complete by approximately 

12,000 years ago, the late glacial period was marked by massive landform change, including rapid 

deposition in lowland valleys and extensive erosion of upland slopes, (Anderson 1990; Anderson and Smith 

1994; Clark and Gillespie 1997; Koehler and Anderson 1994; Pohl et al. 1996). 

At the end of the Pleistocene, the continental ice sheets melted causing oceans to rise rapidly 

(eustatic sea level rise).  Between 15,000 and 10,000 years ago, canyons and valleys along the Central 

Coast of California flooded as a result of the new sea level (Kaijankoski et al. 2019).  Rapid rise in sea level 

(approximately 75 meters), followed by sea levels stabilization during the Younger Dryas (12,900–11,500 

cal BP), resulted in the development of bays and estuaries along the coast (Jones et al. 2019; Masters and 

Aiello 2007).  There is some speculation that the estuary was much larger during this time, due to the 

identification of Flandrian estuary mud offshore, approximately one mile from the sand spit barrier (Orme 

1990).   Orme (1990) also suspects a barrier similar to the sandspit must have existed during that time (late 

Pleistocene, early Holocene) for the Flandrian sediments to accumulate.  Additionally, as sea-level rise 

slowed, sedimentation increased replacing tidal flats, marshes, and lagoons with bays and inlets, such as 

Elkhorn Slough, Morro Bay, and Halcyon Bay (Pismo Beach; Atwater 1979; Atwater et al. 1977; Bickel 

1978; D. Jones et al. 2002; Jones and Waugh 1997; Mikkelsen et al. 2000; Wells and Gorman 1995; West 

1988, 2000). 



29 
 

The environment adapted to warmer temperatures of the beginning Holocene, in Morro Bay 

coniferous trees were replaced with oak woodland, chaparral, and coastal sage (Jones et al. 2019; West 

et al. 2007).  Sea temperatures cooled from 9000 to 4800 cal BP which intensified the offshore current 

increasing marine productivity (Jones et al. 2019).  Rosenthal and Meyer (2004) argue that a rapid colluvial 

deposit was followed by a period of landform stability which is represented by buried soils in the alluvial 

valleys of the Diablo Range and adjacent lowlands.  These buried soils suggest that after deposition, the 

landform remained stable throughout the remainder of the Middle Holocene. 

West (2000) records pollen samples suggesting that conditions resembled modern climatic 

conditions during the Late Holocene.  Precipitation is very variable after 3000 cal BP, with two periods of 

major drought, called the Medieval Climatic Anomaly (MCA).  The MCA was identified by the low stands of 

Mono Lake between 1100 and 890 cal BP and 790 and 650 cal BP (Stine 1994).  The drought period is 

represented across the west and resulted in extreme resource stress (Graumlich 1993; Jones et al. 1999; 

Waechter and Andolina 2005).  Periods of soil stability and sediment deposition in the fans and floodplains 

are indicated by localized depositional events throughout the valleys of the Coast Ranges recorded 4000, 

2800, 1300, and 650 years ago (Rosenthal and Meyer 2004:26).  The fluctuation in stability could be a 

response to a change in vegetation coverage due to irregular precipitation possibly influenced by climate 

change.  

In Morro Bay, the cooler temperatures of the middle and late Holocene, allowed for habitat stability 

(Gallagher 1996).  But Gallagher (1996) argues that core samples from the estuary allude to a sudden 

deepening of the bay possibly caused by seismic activity.  Jones et al. (2019) hypothesizes that this activity 

caused habitat devastation resulting in an occupational hiatus in the Morro Bay region.  The following 

section will focus on the evolution of the estuary and bay. 

3.3 Evolution of the Estuary 

 There is uncertainty as to when Morro Bay’s estuary was formed, but based on radiocarbon data 

from similar environments it is thought to have been formed during the Holocene between 5,000 and 3,000 

years ago (Figure 6; Far Western 2016).  Based on the bathymetry and relative sea level, the shoreline 



30 
 

was approximately 6 to 10 kilometers west of the present coastline during the Pleistocene (Figure 6; Simms 

2015; Gibson 1992).  Over time, with increased sedimentation and the leveling of sea-level rise, a low 

barrier was created, blanketing the exposed rocky shelf.  This barrier helped to foster perfect estuarine 

conditions for a lagoon.  Later, the barrier shifted east and was eventually augmented by dune sands, which 

were gradually stabilized by vegetation (Orme 1991).  

 Past scholars have noted that the bay’s changing environment over time required plants and 

animals to adapt (e.g., Gibson 1992; Jones et al. 1994; Mikkelsen et al. 2000).  Jones et al. (1994:178) 

report that a relatively mature mud-flat could have lined the embayment as early as 8100 cal BP based on 

finding invertebrate remains (e.g., Macoma, Tresus, and Saxidomus species) at a nearby site.  The estuary 

could have been at its greatest expanse during the Early Period, around 5500 cal BP (Kaijankoski et al. 

2019). This claim is further supported by an increase of Pismo clam (Tivela stultorum), suggesting that the 

formally rocky shores had been replaced with sandy beaches (Jones et al. 1994:178).   

There is debate as to how the estuary evolved during the Middle Period (2600–1000 cal BP).  Some 

scholars speculate that there was an occupational hiatus during the Middle Period due to a lack of sites 

with dates of this time (Jones et al. 2019).  Jones et al. (2019:246) argue that seismic activity could have 

“shut the estuary off from the sea and caused sudden deterioration of [the] shellfish habitat.”  There is also 

speculation as to whether this caused increased siltation within the bay resulting in a decreased fish 

population.  Fish species collected from the excavations described in this thesis allude to a healthy bay 

condition as many identified species are known to inhabit the bay and estuary.  Approximately 1100 cal BP, 

a smaller estuary is noted to have formed, however shellfish frequencies are significantly lower, and fish 

remains even fewer in sites dating to the time period (Jones et al. 1994).   

Today, Morro Bay is part of larger Estero Bay, which is bound by Los Osos, Morro Bay, and 

Cayucos.  Morro Bay’s most notable landmark to the west, Morro Rock, sits north of the harbor mouth.  In 

1913, the Army Corps of Engineers artificially connected Morro Rock to the mainland during a massive 

harbor development project.  Based on historic maps, Morro Creek used to flow into the bay (Figure 7).  But 

eventually Morro Creek was diverted to flow into the ocean, where it currently flows today.  There is 

speculation that Morro Creek meandered between its historic location and current location due to a small 



31 
 

water source noted on a historic map from 1883 (Figure 7).  This water source is nicknamed “Sperm Lake” 

due to its shape.  The location of Sperm Lake on the historic map suggests that Morro Creek, historically, 

may have meandered between the ocean and the bay.  The change in the location of Morro Creek could 

have been caused by sedimentation, as discussed in Chapter 2, but dune development could have also 

diverted the creek.  Dune development raises the base level of waterways which can cause the waterway 

to reroute.   



32 
 

Chapter 4: Regional Cultural Context and Ethnography 

The following chapter provides a brief summary of the regional culture-historical sequence of the 

Central Coast made up of a series of temporal periods.  The establishment of a region-specific chronology 

is vital to the development of research questions related to the understanding of human behavior and 

change over time.  The Central Coast sequence is the most-widely accepted chronology of San Luis Obispo 

County (Jones 1995, 2003; Jones et al. 2007, 2019).  This chronology, implemented from San Simeon to 

Point Conception, has evolved over many years of archaeological research and advancement (Table 1: 

Central Coast Sequence below).   

Below, the current chronology is outlined first, followed by a brief discussion of the research area’s 

cultural and ethnographic context of Morro Bay.  Next, a discussion of the importance of including an 

ethnographic context in any research project is explored.  Last, past archaeological research and studies 

at CA-SLO-16 will be provided. 

4.1 The Central Coast Sequence  

 The Central Coast sequence was first proposed by Jones (1993) and has been refined with the 

advancement of archaeological research and dating methods (Jones et al. 2007; Jones and Ferneau 

2002a).  To divide time into temporal periods, researchers use radiocarbon dates and temporally assigned 

artifacts to delineate each period. In turn, changes in human behavior over time can be identified and 

examined.   

Morro Bay has a relatively limited sample of radiocarbon data, therefore researchers have had to 

rely on data collected in neighboring regions (e.g., San Luis Obispo, San Simeon, Big Sur; Jones et al. 

2019), or diagnostic artifacts, to delineate certain periods of time.  One artifact that is considered a reliable 

dating source is the Olivella (cf. Callianix) shell bead.  After years of analysis, researchers have assigned 



33 
 

a complete temporal series to Olivella shell beads5 which can be used to decipher the temporal components 

of an archaeological site (Milliken and Schwitalla 2012).   

The following sections will include temporally diagnostic artifacts that are associated with each 

temporal period, including the Olivella (Callianax biplicata) shell bead types, and cultural patterns, 

settlement types, and a sample of San Luis Obispo County sites associated with the temporal period.  

Please refer to Figure 8 for proximity to Morro Bay for each site described.   

Table 1: Central Coast Sequence 

Period Subperiod Years cal BP Additional Information 

Post Contact  180–Present  

Late  700–180  

 Protohistoric 450–180  

Middle/Late Transition  950–700  

Middle  2550–950  

 Late Middle 1550–950 Adapted from King (1990) and Lambert (1994) 

 Early Middle 2550–1550 Adapted from King (1990) and Lambert (1994) 

Early  5700–2550  

Millingstone/Lower Archaic 10,000–5700  

(Adapted from Jones et al. 2019:29) 

Millingstone Period (10,000-5500 cal BP)  

There is limited evidence (e.g., fluted points; CA-SLO-2, CA-SLO-1797) of human occupation as 

early as 13,000 years ago in San Luis Obispo County (Gibson 1996; Jones et al. 2019; Mills et al. 2005; 

Rondeau et al. 2007). Jones et al. (2019:37) argues that the earliest “substantive evidence for human 

occupation [in San Luis Obispo County] dates to 10,300 years ago.”  Millingstone Period, or Lower Archaic, 

assemblages are commonly identified by their abundance of milling slabs, handstones, and cobble-core 

tools, (Jones et al. 2019; Kaijankoski et al. 2019).  Jones et al. (2019:37) note thick, rectangular, L-series 

Olivella shell beads could have occurred during this time, but very few have been recovered in this temporal 

context in this region.

 
5 For a more detailed explanation please refer to Milliken and Schwitalla’s (2012) California and Great Basin Olivella 
Shell Bead Guide.  



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San Luis
Obispo

San Simeon

Whale Rock

Coon Creek

Piedras
Blancas

Santa
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Lodge Hill

Cross
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Lake Nacimiento

San
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Estero
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Santa
Margarita

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San
Luis

Obispo
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M O N T E R E Y
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S A N  L U I S
O B I S P O  C O U N T Y

Camp Roberts

Montaña
de Oro SP

Oceano
Dunes

P a c i f i c
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Area of Potential Effects (APE)

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Kilometers

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 H

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Figure 8: San Luis Obispo County Region

(Provided with permission from Far Western) 34



35 
 

Scholars note a high intensity of shellfish exploitation with terrestrial game and marine mammals 

contributing minimally to archaeological deposits in most locations (Hildebrandt et al. 2010; Jones et al. 

2008).  Additionally, as indicated by the temporal period’s name, collection and processing of plants, seeds, 

and other botanicals were an important pursuit during this period and are reflected in the archaeological 

record (Hildebrandt et al. 2010). 

There are a few well-studied archaeological sites within the county that have a Millingstone Period 

component.  These sites include Cross Creek (CA-SLO-1797) northeast of Pismo Beach in Edna Valley 

(Fitzgerald 2000; T. L. Jones et al. 2002); CA-SLO-832 at Pismo Beach (D. Jones et al. 2002); CA-SLO-2 

(arguably one of the most studied Millingstone Period sites) and CA-SLO-585 at Diablo Canyon 

(Greenwood 1972; Jones et al. 2008, 2009).  Additionally, there are inland sites in the Upper Salinas Valley 

(Fitzgerald 1997; Stevens et al. 2004); and near Camp Roberts (Alvarez 2009).  There is also a Millingstone 

Period component documented at Morro Bay site CA-SLO-165 (Mikkelsen et al. 2000), located just 0.1 

miles northeast of the current study area.   

Early Period (5500-2500 cal BP)  

In San Luis Obispo County, there is extensive evidence for human occupation during the Early 

Period (5500-2500 cal BP; T. Jones et al. 2019; D. Jones et al. 2012).  Many scholars (Basgall 1987; Jones 

and Waugh 1997; Mikkelsen et al. 2000) suggest there was a substantial increase in population during the 

Early Period, based on these findings.  There is also a debate within the discipline that shifts in technology 

during this time suggest the introduction of an outside population (Harrison 1964; Lathrop and Troike 1984; 

Warren 1968;).  Other scholars argue that these advancements are attributed to local communities' 

technological development and evolvement (Erlandson 1997; Glassow 1997).   

Researchers acknowledge that increased population requires a more diverse and intensive 

resource source. Basgall (1987) argues that the introduction of mortars and pestles suggests a more 

intensive use of acorns to support the increased population.  While Jones and Waugh (1997) argue that 

populations began storing resources, such as acorns, allowing for more sedentary settlements.  There was 

also an increase in hunting tools, including Rossi square-stemmed projectile points, large side-notched 



36 
 

points, and contracting-stemmed points.  Bead types attributed to the Early Period include thick, 

rectangular, L-series Olivella beads and steatite beads (Gibson and Koerper 2000; Milliken and Schwitalla 

2012). 

Sites with a well-defined Early Period component are more commonly identified along the coast 

than the interior in San Luis Obispo County.  Mikkelsen et al. (2000) suggests that this regional site 

distribution could have been due to the effect drought conditions had on coastal resources during the Middle 

Holocene (e.g., coastal estuaries; see Hildebrandt 1997a, 1997b). Coastal sites with an Early Period 

component include Little Pico sites CA-SLO-175 and CA-SLO-1259, the Lodge Hill area sites CA-SLO-369, 

CA-SLO-383, and CA-SLO-697, CA-SLO-264 at Piedras Blancas, and CA-SLO-273 and CA-SLO-274 at 

Arroyo de los Chinos also produced Early Period assemblages (Hildebrandt et al. 2002; Jones and Ferneau 

2002a; Jones and Waugh 1995).  Just south of Morro Bay, in Los Osos, there are a few Early Period sites 

including CA-SLO-23, CA-SLO-458, CA-SLO-812, and CA-SLO-1795 (Jones et al. 2019:225).  In Morro 

Bay, CA-SLO-165 has an extensive Early Period component.  Research also suggest that inter-group 

exchange increased during this time as a result of increased intensification focused on the procurement of 

low-rank/high-cost resources, such as acorns, which is reflected by the increase of obsidian importation in 

the archaeological record (Jones and Waugh 1997).   

Middle Period (2500-1000 cal BP)  

Although the Middle Period is “highly visible in the central California coast,” San Luis Obispo County 

has a few areas of nonconformity (Jones et al. 2019:39).  In San Simeon, just a few miles north of the study 

area, Joslin (2006, 2010) reports a few sites with strong Early and Late components and missing Middle 

Period components.  This is also true of Morro Bay.  Only four Morro Bay sites, CA-SLO-14, CA-SLO-165, 

CA-SLO-2222, and CA-SLO-978, show any evidence of occupation during the Middle Period. Site CA-SLO-

14 has yielded two dates of 2300 cal BP, while CA-SLO-165 and CA-SLO-978, have produced questionable 

dates.  Olivella saucer beads recovered from an Early Period context at CA-SLO-165 resulted in two 

calibrated dates of 2300 and 2000 cal BP (see Mikkelsen et al. 2000).  Similarly, CA-SLO-978 yielded mixed 

dates of 1900 and 1100 cal BP.   



37 
 

Sites with a well-dated Middle Period component in San Luis Obispo County include San Simeon’s 

CA-SLO-175 and CA-SLO-267 (Jones and Ferneau 2002a; Jones and Waugh 1995) and Santa Margarita’s 

CA-SLO-586, CA-SLO-1644, and CA-SLO-2518 (Farquhar et al. 2010; Fitzgerald 1997b; Wickstrom et 

al.1996).  Scholars have suggested that a few important adaptations occurred during the Middle Period, 

noting a decreased dependence on shellfish and an increased intensification of processing and exploitation 

of acorns (Jones 2003; Jones and Waugh 1995, 1997).  Jones and Ferneau (2002a) suggest that the 

intensification of acorns could have been a continuing trend from the Early Period and the reason for an 

increased use of mortars and pestles.  Additionally, data gathered through obsidian hydration suggests that 

exchange of Coso and Casa Diablo obsidian from eastern California reached peak proportions during this 

temporal period (Bouey and Basgall 1991; Jones 1995, 1996). 

I agree with Jones et al. (2019:39) who argue there is value in dividing the Middle period into 

phases.  Jones compares this practice to that of King (1990), in the Santa Barbara area, who divided the 

Middle Period into five phases (M1-M5).  The separation of this temporal period allows researchers to better 

understand changes in human movement, behavior, and environmental impacts during the Middle Period.  

Lambert (1994) simplified the phases to two: Early and Late Middle Period.  Jones equates the Early Middle 

Period of the Central Coast sequence (2600-1500 cal BP) with Lambert’s phases M1 and M2, while the 

Late Middle Period (1500-950 cal BP) “[correlates] approximately with his phases M3-M5” (Jones et al. 

2019:39). 

The separation of the Early Middle Period and the Late Middle Period is vital to the understanding 

of change in human occupation in Morro Bay. Jones et al. (2019) identifies two “gaps” of occupation in 

Morro Bay during the Middle Period.  The first gap overlaps the beginning of the Early Middle Period, 2900-

2300 cal BP, and the second occurs during the Late Middle Period, 1700-1100 cal BP (Jones et al. 2019).  

Jones et al. (2019) attributes the gaps in the radiocarbon record to seismic activity in the bay area heavily 

citing Gallagher (1996).  Jones et al. (2019:250-251) alludes to severe seismic activity that caused habitat 

deterioration, a sudden deepening of the bay (Gallagher 1996), human populations to evacuate the area, 

and the estuary to be shut off from the sea (Jones et al. 2019:246).  The Late Middle Period gap will be 

referred to throughout this research.  



38 
 

Due to the lack of Middle Period components in Morro Bay, researchers have applied regional data 

to allude to changes in the archaeological record during this time.  The most common markers are Olivella 

shell beads; types include saucer beads (class G), specifically normal (G2) and irregular (G6). “Haliotis disk 

ornaments, perforated disks, rings with incised edges, and plain- and flat-ended rings” appear during this 

period (Jones et al. 2019:39; also, Jones 1995).  Large side-notched and Rossi square-stemmed projectile 

points disappear, as do rectangular L-series Olivella beads (Jones et al. 2019).  It is debated whether large 

concave-base points appear during this time as they are “rare on the Central Coast and not securely dated” 

(Jones et al. 2019:38).  Contracting-stemmed projectile points are also noted during this period (Jones et 

al. 2007:136; Wiggins 2022) although this type of point spans across several temporal periods.  Grooved 

stone net weights and curved shellfish hooks appear, in addition to bone tools such as needles, pins, awls, 

whistles, spatulas, gorge hooks, and antler tines (Jones et al. 2019). 

Middle-Late Transition (1000-700 cal BP)  

The Middle-Late Transition experienced Medieval droughts, settlement disruptions, and a debated 

decline in population.  The San Luis Obispo County coast differs from neighboring coastlines, (e.g., Santa 

Barbara; Arnold 2001), in that evidence for archaeological materials during the Middle-Late Transition 

declines. Some scholars suggest this may reflect a more dispersed pattern of settlement, while others 

attribute the decline to environmental degradation and resulting decline in human population densities due 

to the severe Medieval dry period, also referred to as the Medieval Climatic Anomaly (1150-600 cal BP; 

Graumlich 1993; Jones 1995; Jones et al.1999; Stine 1994).   

 Coastal deposits dating to this temporal period include the Coon Creek Site CA-SLO-9 (Codding 

and Jones 2007), Little Pico Creek CA-SLO-175, and CA-SLO-165 and CA-SLO-239 in Morro Bay.  CA-

SLO-536 is a large Middle-Late Transition site in the Chorro Valley.  While just north of Morro Bay, Cayucos 

has at least three sites that date to the Middle-Late Transition including CA-SLO-74, CA-SLO-879, and CA-

SLO-2195 (Wiggins 2022:132). Due to the increase in fish remains during the Middle-Late Transition in the 

CA-SLO-9 deposit (Codding and Jones 2007; Codding et al. 2009, 2010) and in San Simeon (Joslin 2010), 

scholars argue that the severe effects of drought on terrestrial landscapes led populations to exploit marine 

resources.  Jones (1995) states that obsidian exchange networks collapsed during this time as obsidian 



39 
 

declined dramatically in the archaeological record.  Archaeological constituents attributed to the Middle-

Late Transition include contracting-stemmed, small leaf, and double side-notched projectile points, curved 

shellfish hooks, hopper mortars, and a variety of Olivella shell bead types (B2, B3, G1, G6, K1, and possibly 

D1; Jones and Waugh 1995). 

Late Period (700 cal BP – Historic Contact)  

Radiocarbon data and accompanying deposits for the Late Period alludes to more mobile and 

dispersed settlements with a higher population density than previous temporal periods (Jones et al. 2019).  

Originally, researchers thought settlements were isolated to terrestrial landscapes, but excavations in Big 

Sur have identified seasonal or temporary camps on the shore (Hildebrandt and Jones 1998; Jones 2003; 

Wohlgemuth et al. 2002). Subsistence practices during the Late Period are still focused on acorn processing 

and marine resources with an increase of marine shellfish and the addition of plant and terrestrial foods, 

specifically deer (Bouey and Basgall 1991; Jones 1995; Jones et al 2019).   

Deposit constituents continuing from the Middle-Late Transition include hopper mortars, milling 

slabs, handstones, circular shellfish hooks, and Olivella shell beads (types B2, B3, G1, G6, and K1; Jones 

et al. 2019:40).  New constituents include the Desert Side-notched and Cottonwood arrow points, chipped 

stone bead drills, flowerpot mortars, clamshell disk beads, Haliotis disk beads, Olivella shell bead types E1 

and E2, and steatite disk beads (Jones et al. 2019).  The most notable development during th