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Geology, tephrochronology, radiometric ages, and cross sections of the Mark West Springs 7.5' quadrangle, Sonoma and Napa counties, California

Scientific Investigations Map 2858

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Abstract

The purpose of this geologic map is to provide a context within which to interpret the Neogene evolution of the active strike-slip fault system traversing the Mark West Springs 7.5' quadrangle and adjacent areas. Based on this geologic framework, the timing and total amounts of displacement and the Neogene rates of slip for faults of the right-stepover area between the Healdsburg and Maacama Faults are addressed.

The Mark West Springs quadrangle is located in the northern California Coast Ranges north of San Francisco Bay. It is underlain by Mesozoic rocks of the Franciscan Complex, the Coast Range ophiolite, and the Great Valley sequence, considered here to be the pre-Tertiary basement of the northern Coast Ranges. These rocks are overlain by a complexly interstratified and mildly to moderately deformed sequence of Pleistocene to late Miocene marine and nonmarine sedimentary and largely subaerial volcanic rocks. These rocks and unconformably overlying, less-deformed Holocene and Pleistocene strata are cut by the active right-lateral Healdsburg and Maacama Fault Zones.

Mapping of the Mark West Springs quadrangle began in 1996 and was completed in October 2002. Most of the mapping presented here is original, although a few other sources of existing geologic mapping were also utilized. Funding for the project was provided by the National Cooperative Geologic Mapping and Earthquake Hazards Reduction programs of the U.S. Geological Survey, in cooperation with geologic hazards mapping investigations of the California Geological Survey.

Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Geology, tephrochronology, radiometric ages, and cross sections of the Mark West Springs 7.5' quadrangle, Sonoma and Napa counties, California
Series title:
Scientific Investigations Map
Series number:
2858
Year Published:
2004
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Description:
2 sheets, 48 by 36 inches; 16 p. pamphlet; datafiles
Scale:
25000