Northern Coast Ranges

Abstract The California Northern Coast Ranges include the mountainous and semimountainous areas and intermontane valleys from the Oregon-California boundary on the north to San Francisco Bay on the south. The west boundary is the Pacific Ocean and the eastern boundary is an arbitrary sinuous line which approximately follows the Southern Pacific Railway from Oregon southward to a point about 10 miles southwest of Redding, thence approximately along the western limits of the Cretaceous of the Sacramento Valley Province to a point a few miles northeast of Napa, and thence southward to Carquinez Straits. This province lies between 37°48′ and 42° North Latitude and i22°17′ and 124°23′ West Longitude. It has an approximate area of 19,938 square miles, of which about 8½ per cent, or 1,700 square miles, is underlain by sedimentary rocks of types common to oil-field provinces. This total of 1,700 square miles is made up of a number of widely separated areas, in many of which the basement is shallow, ranging in depth from a few hundred to 4,000 feet. The greatest estimated thickness of sediments is in the Eel River Basin, Humboldt County, where formations of Pliocene and Miocene age total about 12,000 feet. The calculated volume of sediments of the California Northern Coast Ranges, which might be placed in the classification of possible future oil provinces, is 500–550 cubic miles. A comparatively thin mantle of Quaternary and Pleistocene masks parts of the area, and as at least a part of the Petaluma formation (Pliocene) in the Petaluma