Geoarchaeological Investigations at a Stege Mound (CA-CCO-297), a Late Period Shellmound: A Study of Archaeological Site Formation and Paleoenvironment Reconstruction along the San Francisco Bay Estuary, California

Purpose of the Study: This thesis investigates the influence of paleoenvironmental conditions on prehistoric cultural occupation at CA-CCO-297, a Late Period Ohlone village site. A recent cultural resource management project conducted at the site made it possible to research CCO-297's cultural and natural deposits that were extracted from column and core samples. The purpose of this thesis is to examine those sediments for evidence of a cultural response to environmental change along the San Francisco Bay estuary.

Methods: This study incorporates archival research with field-based and laboratory techniques. Field-based techniques include the excavation, recording, and interpreting of stratigraphic profiles, and the collection of column and core samples for laboratory analysis. Laboratory techniques conducted on the samples include loss on ignition, magnetic susceptibility, phosphorus, potential of hydrogen, macrofossil and microfossil analysis. The combination of archival research, fieldwork, and accompanying laboratory procedures produces data sets useful for the paleoenvironment reconstruction and reveal natural site formation processes.

Findings: Site CCO-297 is situated on a terrestrial landform on the edge of a tidal creek during the sites initial occupation in 1350 cal AD. A reconstruction of the paleoenvironment reveals that a tidally influenced brackish marsh was at its peak in evolution shortly before occupation of the site began, with the peak of the marsh occurring soon after 1203 cal AD. The marsh was initially formed by a strictly freshwater inflow. The peak of the marsh's formation and the initial occupation of the site closely coincide with the transition of the Medieval Climatic Anomaly (MCA) to the Little Ice Age (LIA) that is estimated to have occurred from 1350 to 1450 cal AD.

Conclusions: Formation of prehistoric shellmound site CCO-297 directly correlates with the dynamic evolution of a tidally influenced brackish marsh along the San Francisco Bay estuary during the late Holocene. The results of this research place CCO-297 into the context of an evolving paleo-landform, one that was affected by shifting climatic periods from the MCA to the LIA. This thesis shows how environmental factors influenced archaeological site formation processes during the Late Period along the San Francisco Bay estuary.