Bay Area Geography and Geology, Figure 1

Geologic sketch map of the northern Coast Ranges, central California, showing faults with Quaternary activity and basin deposits in northern section of the San Andreas fault system. Fault patterns are generalized, and only major faults are shown. Several Quaternary basins are fault bounded and aligned parallel to strike-slip faults, a relation most apparent along the Hayward—Rodgers Creek—Maacama fault trend.

	Alluvial and estuarine deposits (Quaternary)--chiefly basin fill; may also include some Pliocene deposits.
	Clear Lake Volcanics (Quaternary and Tertiary)--flows, tuffs, and breccias of dacite and rhyolite and less abundant basalt. Age is late Pliocene to Holocene.
	Bedrock (Tertiary and older)--varied rock types
____ _ _ _	Fault exhibiting evidence of Quaternary displacement--dotted where concealed by water.

Source: USGS Professional Paper 1515, p.85.

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updated April 3, 2002