220 SOUTHERN CALIFORNIA GEOLOGY 



AGE OF THE TRANSVERSE FAULTS 



The east-west extending faults of the Transverse 

 system are assumed to be newer than the first North- 

 westerly and Northeasterly Groups, which are cut out 

 by them. As a generalization it may be said that the 

 north-south trends of California — those of the Basin 

 and Coast Ranges — have been cut directly across and 

 out by the great rifts of the east-west group. From 

 the fact that the east-west rifts are cut out by the 

 north 65° west-extending San Andreas-Puente Belt 

 and the north 45° west San Jacinto fault we presume 

 that they are older than the second Northwest groups. 



The older northwesterly-extending folds of Miocene 

 strata seen on the east end of the Santa Monica Range, 

 were cut across by a revival of movement along 

 the east-west-extending Santa Monica fault in early 

 Pleistocene time, and the folds in turn are cut across 

 by the later northwest faults. 



There is a suggestion that some of the east-west 

 rifts of the San Gorgonio Pass were initiated before 

 the deposition of the Badlands strata which contain 

 fossils of Pleistocene and Recent time. Some of these 

 faults outlined the north end of the Peninsula Ranges 

 and the Pass itself. It is evident that they date back 

 to Miocene time or before, although later renewals of 

 movement along them have taken place locally. 

 RELATIVE AGES OF THE NORTHWEST GROUPS 



The ages of the Northwest-trending Structures 

 range from Pliocene to Recent, On a previous page 

 it has been confessed that this provisional classifica- 

 tion is merely a makeshift one. The trends may have 

 prevailed both before and after those of the east-west 

 directions and therefore are of, at least, two ages. The 



