Quaternary geology of Alameda County, and parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and San Joaquin Counties, California: A digital database

Alameda County is located at the northern end of the Diablo Range of
Central California. It is bounded on the north by the south flank
of Mount Diablo, one of the highest peaks in the Bay Area, reaching
an elevation of 1173 meters (3,849 ft). San Francisco Bay forms the
western boundary, the San Joaquin Valley borders it on the east and
an arbitrary line from the Bay into the Diablo Range forms the
southern boundary. Alameda is one of the nine Bay Area counties
tributary to San Francisco Bay. Most of the country is mountainous
with steep rugged topography. Alameda County is covered by
twenty-eight 7.5' topographic Quadrangles which are shown on the
index map (alq_quad or Sheet 2).
The Quaternary deposits in Alameda County comprise three distinct
depositional environments. One, forming a transgressive sequence
of alluvial fan and fan-delta facies, is mapped in the western
one-third of the county. The second, forming only alluvial fan
facies, is mapped in the Livermore Valley and San Joaquin Valley in
the eastern part of the county. The third, forming a combination
of Eolian dune and estuarine facies, is restricted to the Alameda
Island area in the northwestern corner of the county.