94 SOUTHERN CALIFORNIA GEOLOGY 



scribed. Beneath the domes of this range almost price- 

 less pools of oil have been found in recent years which 

 have added vastly to the wealth of Southern California. 

 The other ranges alluded to are well known and space 

 forbids their further mention here. 



THE DOWNEY VALLEY PLAIN 



I use the name of Downey Valley Plain for the long- 

 est and largest of the Southern California valley plains. 

 It borders the west side of the north end of the 

 Peninsular Highland, and is a structural accompani- 

 ment of the last mentioned feature. The Downey 

 Plain is often miscalled "the Coastal Plain of South- 

 ern California" and sometimes the "Los Angeles 

 Basin." It extends southeast from the south side of 

 the Santa Monica Range near Sherman in western 

 Los Angeles for sixty miles to near San Juan Capis- 

 trano. It is bordered on its seaward side by the 

 Dominguez and San Juan Ranges and on its north and 

 northeast sides by the east end of the Santa Monica 

 Range, the Elysian Park, Repetto and Montebello Hills 

 and the Puente and Santa Ana Ranges. In size it is 

 comparable to the largest of the Foothill Valleys and 

 is the site of many flourishing farms and towns, in- 

 cluding Los Angeles in part, Huntington Park, Fuller- 

 ton, Anaheim, Santa Ana and other cities. The Ciegna, 

 La Brea and Sherman Flats in south and west Los 

 Angeles are the northwest extensions of this plain. 



The valley floor is somewhat synclinal in structure 

 with subordinate folds and the strong Puente Fault 

 zone along its northeast side. Its substructure to 

 depths of 4000 feet or more is strata of Pliocene and 

 Pleistocene ages. Its surface is largely covered by 



