134 SOUTHERN CALIFORNIA GEOLOGY 



(Hathaway formation of Francis Vaughan), which 

 have been uplifted to that extent on the west side of 

 the north-south fault zone. 



THE NORTHWESTERLY FAULT BELTS 



Faults and rifts of this direction occur throughout 

 a wide belt of the westerly half of North America, 

 and largely south of the Transverse Belt on either 

 side of the Mexican border, between the Santiago 

 Range of the Trans-Pecos Texas Region on the east 

 and the west margin of the continental shelf on the 

 west. There are conspicuous instances of the north- 

 westerly faults cutting out the north-south trends at 

 El Paso, Texas, and other places. 



There is some suggestion from the data which I 

 now possess that there have been two or more epochs 

 in Southern California when northwesterly structural 

 trends prevailed, or, as may otherwise be stated, that 

 the Basin Range epoch of dominant north-south 

 trends was succeeded by an epoch of northwest trends ; 

 the latter, in turn, by an epoch of east-west structures, 

 after which another epoch of the faulting in northwest 

 directions may have occurred. This theory implies 

 that one of the groups of northwest structures pre- 

 ceded the east-west Transverse structures, and that 

 the other succeeded it. The possibility of such a se- 

 quence is suggested by the relations of the east-west 

 faulting to older northwesterly folds which lie across 

 the east end of the Santa Monica mountains in the 

 City of Los Angeles and elsewhere and by the fact that 

 the latter structures are in turn cut across by a later 

 set of northwesterly faults of the Puente system. 



In general, however, I wish to say that the divi- 



