The Los Angeles region of southern California (Fig. 35) is situated between North Latitudes 33° 22′ and 34° 14′ and West Longitudes 117° 36′ and 119° 11′. It is bounded on the north by the Santa Monica and San Gabriel Mountains, on the east by the Perris Block and Santa Ana Mountains and on the southwest side by the Pacific Ocean. Part of the region underlies the ocean floor. Its longest dimension, which trends northwest, is approximately 60 miles and it averages about 25 miles in width.

This region covers approximately 1,940 square miles, of which about 1,440 square miles forms the Los Angeles Basin and is underlain by a thick section of sedimentary rocks with maximum thickness probably 25,000 feet. It is estimated that the basin contains 1,900 cubic miles of sediments above 20,000 feet and 350 cubic miles of strata below that depth. Of this rock volume, approximately 10 per cent, or 225 cubic miles, is continental in origin, nearly all of which is Pleistocene and Recent in age; but it also includes a small amount of Vaqueros redbeds (lower Miocene). These figures are necessarily rough estimates as the deepest part of the basin has not been penetrated by the drill. The culture of the district prohibits the use of heavy charges of dynamite in seismic work to bring up reliable deep reflections to verify depth to the basement complex in the structurally deep area.

The status of the Los Angeles Basin as a petroliferous province is well