T15 Lakes Past, Present, and Future—Archives of Climate Variability, Paleoenvironment, Geohazards, and Economic Resources I

Sunday, 9 October 2022
8:00 AM - 12:00 PM
607

BURIED BY WATER AND SAND: GLIMPSES INTO THE HOLOCENE LANDSCAPE AND PALEOECOLOGY OF PREHISTORIC SAN FRANCISCO

Paper number: T15-14
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

The landscape of modern San Francisco represents a highly transformed and urbanized environment, as the population explosion following the Gold Rush of 1849 resulted in significant landscape alterations as historic dune fields were leveled and creeks, lakes, and tidal wetlands filled to support the expanding city. Thus, our understanding of ecosystem resources available to indigenous groups prior to this dramatic transformation is limited.

Archaeological investigations conducted for new construction are providing a unique opportunity to reconstruct this lost landscape. We discuss paleoecological data extracted from multiple wetland paleosols preserved beneath the modern neighborhoods of Yerba Buena and South of Market. The paleosols, which lie at depths up to 15 m below modern surface, were subsampled for palynological and macro-botanical analyses and radiocarbon dating.

The oldest paleosol dates to 6,700 cal B.P., and represents the terrestrial shoreline surface before early Holocene sea level transgression. The vegetation comprised a rich herbaceous assemblage suggestive of coastal dune and foredune communities.

The other wetland paleosols are late Holocene in age and represent a diverse array of wetland habitats and resources, although their persistence was transitory due to dune migration. For instance, wetland paleosols were examined at a site on Van Ness Avenue where each paleosol, separated by ~3 m of dune sands, indicates very different wetland environments developed on three occasions. Initially, a moist seep prevailed with Morella and an understory of ferns at 2060 cal B.P. This was buried by dunes until 1930 cal B.P. when a pond (Potamogeton) and freshwater wetland (Cyperaceae) persisted. This was subsequently overlain by dune deposits until 1220 cal B.P. when riparian vegetation (Salix) was established for a short period.

These and other findings will be placed in the context of regional environmental and climatic changes.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-378053

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