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Ancient Processes at the Site of Southern San Francisco Bay: Movement of the Crust and Changes in Sea Level
Brian F. Atwater, U.S. Geological Survey
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January 1, 1979
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ABSTRACT:
Several kilometers of sea water probably covered the site of San Francisco Bay 150 million years ago. Motion of lithospheric plates fostered sedimentary and structural accretion that subsequently transformed this oceanic abyss into a landmass. The current episode of right-handed movement along the San Andreas fault reflects sideways motion between lithospheric plates that began locally during the past 10-15 million years. Concurrent vertical movement in the vicinity of the Bay, though at least 20 times slower than displacement along the San Andreas fault, probably created the bedrock trough that now contains much of the Bay and closed a strait that once linked the site of the Bay with the Pacific Ocean. Sediment beneath the floor of the Bay suggests that at least four ephemeral estuaries have occupied the site of the Bay during the past 700,000 years. These estuaries presumably reflect global fluctuations in sea level caused by exchange of water between oceans and continental glaciers. The present estuary originated when the Pacific Ocean entered the Golden Gate about 10,000 years ago. Most of the growth of this estuary occurred during the next 5,000 years. Sites of human habitation contemporaneous with this episode of rapid submergence have not yet been discovered in central California, perhaps because they now lie beneath the mud and water of San Francisco Bay.
SUGGESTED ONLINE CITATION:
Brian F. Atwater.
1979.
Ancient Processes at the Site of Southern San Francisco Bay: Movement of the Crust and Changes in Sea Level. In: Conomos, T. J., editor. San Francisco Bay: The Urbanized Estuary.
http://www.estuaryarchive.org/archive/conomos_1979
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