Geologic Maps of the Sacramento - San Joaquin Delta, California
DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP MF-1401 UNITED STATES GEOLOGICAL SURVEY GEOLOGIC MAPS OF THE SACRAMENTO - SAN JOAQUIN DELTA, CALIFORNIA By Brian F. Atwater INTRODUCTION The Sac ramen to - San Joaquin Delta, the arm of Helley, and W. R. Lettis improved the manuscript with the San Francisco Bay estuary that reaches into the critical reviews, and Faith Dunham, J. R. Le Compte, Central 'valley of California, differs from typical J. B. Pinkerton, N. J. Tamamian, J. A. Thomas, and coastal-plain deltas in three important respects. Natalie Weiskal helped prepare the maps and text for First, rather than meeting the ocean individually and publication. directly, all major waterways of this delta discharge via a single constricted outlet into a chain of estuarine bays and straits. Second, in the most SKETCH OF DEPOSITIONAL HISTORY common vertical sequence of deposits, peat and mud deposited in tidal marshes and swamps (tidal wetlands) The Sacramento - San Joaquin Delta overlies 5-10 directly overlie alluvium or eolian sand, a sequence km of sedimentary deposits. Most of this material, recording a landward spread of tidal environment~ including sources and reservoirs of the Delta's rather than the seaward migration of fluvial natural gas, accumulated in marine environments about environments that is typical of coastal-plain deltas 175 million to 25 million years ago (Burroughs, (Cosby, 1941, p. 43; Thompson, 1957, p. 12; Shlemon 1967). Younger deposits are generally described as and Begg, 1975, p. 259; Atwater and Belknap, 1980). nonmarine (Burroughs, 1967), but some must have formed Finally, intensive human use has led to a peculiar set in shallow seas and estuaries (see maps by C.
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