The Central Coast Ranges are situated between North Latitudes 34° 41′ and 38° 3′ and West Longitudes 119° and 122° 30′ extending from San Francisco on the north to Ventura County on the south and embracing the following minor basins: Livermore, Halfmoon Bay, Salinas Valley, San Andreas Trough, and the Cuyama Valley. The total area of sedimentary rocks is approximately 4,500 square miles and their estimated volume is 6,500 cubic miles. About 75 per cent of the sedimentary rocks are marine.

The generalized geologic map (Fig. 25) shows the thickness of the sedimentary section that is favorable for oil and gas generation and accumulation. In the area west of the San Andreas fault the basement is predominantly granitic but locally the top of the Cretaceous, where present, is considered as basement due to the intensity of deformation and the lack of good source and reservoir beds in the formations of this age. East of the San Andreas fault the top of the Franciscan formation is considered as basement and the overlying Cretaceous is included in the sedimentary section favorable for oil and gas accumulation. This classification is arbitrary but is the most convenient for constructing an isopach map of this type.

The Cuyama Valley, which was barely mentioned as a possible future oil province in the symposium of 1941, has now developed into a major oil-producing province. Subsequent to the first commercial oil strike in January, 1948, in a Norris Oil Company well producing 150 barrels per day of 22°