GEOLOGIC HISTORY 221 



oldest of these were probably associated with the 

 making of the Coast Ranges proper and the Catalina 

 trends of late Miocene or Pliocene time. The later 

 group of the San Andreas type were mostly created 

 in Pleistocene time. 



It is suspected that some of the structures of the 

 older category were prominent in Southern California 

 before their conspicuity was diminished by later 

 events, as, perhaps, in the instances of the older folds 

 which appear with the Santa Monica, tilted fault- 

 blocks. Likewise, some of the faults which are appar- 

 ently of Pleistocene age, may be revivals of movements 

 along pre-existing faults. 



Late rifts of the Northwest groups cut across rifts 

 of all the other groups and bend into the trends of 

 the San Andreas-Puente group. Therefore, it is con- 

 cluded that the latest faulting in California was of 

 this northwest direction. 



EVIDENCE OF PLEISTOCENE AGE IN SOME 

 OF THE MASTER FAULTS 



It is now evident that while the most conspicuous 

 of the master faults mentioned may have originated 

 in more remote epochs they may have had great, 

 if not their greatest, displacements in Ple'stocene time. 



Several of these are known to cut across or to de- 

 form the Pliocene strata and therefore are of post- 

 Pliocene or Pleistocene ages. Some of those that cut 

 Pliocene strata in the hills are covered by more re- 

 cent strata in the valley plains. Hence, we cannot es- 

 cape the deduction that such faults were largely made 

 in the Pleistocene epochs and before the Recent. 

 Among the master rifts, along which there is proof 

 that there was great movement in the Pleistocene 



