The Los Angeles Basin 273 



The Los Angeles Oil Fields 



The Los Angeles oil fields lie within the basin in which the 

 Miocene and Pliocene sands were deposited. The occurrence 

 of petroleum in the porous sands is due to complicated processes 

 of distillation of oil, probably from the innumerable bodies of 

 minute organisms that make up the diatomaceous shales that 

 occur in the formations, and the complex geological changes 

 by which the formations have been upheaved, bent, and frac- 

 tured by the not well-understood forces deep in the earth by 

 which the rocks have been changed. 



Southern California has been much rent and broken by 

 faults. The character of the Los Angeles Basin has been much 

 changed by faulting of the rocks. Faults, or breaks in the 

 rocks, caused by stresses in the crust of the earth have made it 

 possible for oil, distilled by heat and pressure from organic 

 remains in the rocks, to be drained from where it was formed, 

 and to accumulate in porous sand formations. 



Complex Structure of the Los 

 Angeles Basin 



The structure of the basin, which at first seems simple, is 

 in reality somewhat complex. As has been stated, mountains 

 lie to the north and east. The Verdugo Mountains, San Rafael 

 Hills, the Repetto Hills, and the Puente Hills, represent an axis 

 connection between the Santa Monica Mountains to the north- 

 west and the Santa Ana Mountains to the southeast. These 

 mountains or ranges of hills that intervene between the two 

 principal ranges mentioned are upheaved masses, blocks of the 

 earth's crust, bounded by faults or breaks in the rocks. Erosion 

 of the upheaved masses contributed to the sediments that make 

 up the formations by which the basin has been filled. These 

 sediments, originally laid down in essentially horizontal layers, 

 have been disturbed by deep-seated forces, probably the same 

 forces that resulted in the upheaval of the mountains. 



The Los Angeles Basin is bordered on the north, northeast, 



