Sea Level Rise and Shell Mound Inundation within the Islais Creek Estuary, San Francisco, California

Summary

Situated on the southeast edge of San Francisco, the Islais Creek estuary was infilled during early development of the city. Recent geoarchaeological coring searching for prehistoric sites underlying this urban landscape has documented a complex sequence of Holocene landforms deposited as sea level rise transformed the ancestral Islais Creek valley. This exploratory work also identified, in a variety of stratigraphic contexts, an extensive ancestral Native American shell mound that was occupied throughout most, if not all, of the Late Holocene. Sea level reconstruction indicates that the oldest site component was formed just above the tidal range at the time of occupation, was subsequently submerged, and is now situated over 6 meters below surface and overlain by estuarine mud. In response to progressively rising sea levels, later temporal components of this shell mound were formed at increasingly higher elevations. Paleoenvironmental analysis of diatoms and pollen reveal that during the Middle Holocene this estuary was largely freshwater, and transitioned to brackish conditions beginning around 5000 years ago. The timing of this transition raises several new questions regarding the nature of earlier adaptive strategies around the estuary and appropriate techniques for identifying older sites within this deeply submerged and buried landscape.

This Resource is Part of the Following Collections

• Society for American Archaeology 83rd Annual Meeting, Washington, DC (2018)

Keywords

Spatial Coverage

Record Identifiers

Abstract Id(s): 17682