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Original antique geological map of the region around Santa Rosa in the heart of Sonoma County and California's Wine Country. Showing an area of some 100 square miles in size in great detail, this map includes a fascinating look at the geology of the region. Showing topography, settlements, and more, this map is a wealth of information regarding mid-century northern California. The map was produced by the USGS based on information compiled by Charles E. Weaver.

The geology of this region includes many intrusive and extrusive igneous rocks, typical of the coast ranges of central and northern California. These are primarily the so-called "Sonoma volcanics," which dominate the hills to the east and south of Sonoma. Faults, folds, and other geological features are shown.