GEOLOGIC MAP OF THE NAPA 30'x60' QUADRANGLE, NORTHERN SAN FRANCISCO BAY AREA, CALIFORNIA

The Geologic Map of the Napa 30’x60’ Quadrangle, California was compiled from new and existing geologic mapping covering the area between 38° and 38°30' N. latitude and 122° and 123° W. longitude. This map was prepared by the Department of Conservation, California Geological Survey (CGS) and was supported in part by the U.S. Geological Survey (USGS) STATEMAP. New geologic mapping by the CGS was completed in twenty two of the thirty two 7.5’ quadrangles during the period July 1998 to June 2009 with STATEMAP and EDMAP funding. This map is a cooperative effort between the CGS, the USGS, as well as graduate students from San Jose and San Francisco state universities. It covers an area of approximately 2000 square miles of the Coast Ranges geomorphic province of California. Most of the map area is north and west of the San Francisco Bay estuary, which here consists of the San Pablo Bay, the Sacramento River delta and wetlands near Napa and the Fairfield-Cordelia area. The San Andreas Fault traverses the southwestern part of the map marking the active boundary between two lithospheric plates, the North American plate from the Pacific plate lying to the west. The Point Reyes Peninsula is part which of the Salinian block which has been displaced tens to hundreds of kilometers from the southeast by movement along the San Andreas and related faults. Rocks west of the San Andreas Fault are profoundly different than those exposed east of the fault.