SCIENTIFIC BACKGROUND 177 



averages about thirty-two miles and it trends in a 

 direction of about north 65° west. A distinguishing 

 feature of this belt is the fact that its trends are 

 intermediate between those of the Northwest and East- 

 west systems. They are some fifteen degrees more 

 westerly than the almost true-northwest trends of the 

 Northwest system of the San Jacinto type and more 

 than twenty-five degrees more westerly than those of 

 the true Coast Range system of Northern California. 



The master faults of this belt give origin and outline 

 to the following physiographic features: the San Ga- 

 briel Range, most of which is a complicated, uplifted 

 block between the boundaries of the San Andreas and 

 Sierra Madre Faults ; the Puente, Washington, Repetto, 

 Montebello and other hills of folded structures which 

 are bounded on one side by such structures ; and corre- 

 sponding lowland features which have also resulted 

 from these fault displacements. Among these are the 

 La Canada Valley trough, the Bottle-neck Pass at the 

 southwest end of the San Fernando Valley, and pos- 

 sibly, but not proved, the Culver City Pass in the Do- 

 minguez Range. 



The belt is characterized by the occurrence of the 

 following known parallel master rift lines or zones, 

 given in sequence from north to south respectively; 

 San Andreas Rift on the northeast side of the San 

 Gabriel Range, already mapped and thoroughly de- 

 scribed by others; the San Gabriel and Sierra Madre 

 Faults of Kew^ in and along the southwest border of the 

 San Gabriel Range ; the south side fault of the Verdugo 

 Range; and the Puente Fault zone of Arnold and Eld- 

 ridge-, which has been more recently described^ as 



'Bull., U. S. Geological Survey No. 753 ; -309 ; ''768 



