SCIENTIFIC BACKGROUND 129 



northwesterly trends in the middle and later Pleisto- 

 cene epochs. The Garlock fault is apparently older 

 than the San Andreas and newer than the Basin Range 

 faults. 



FURTHER DEFINITION OF THE BELTED 

 GROUPS OF STRUCTURES 

 The belted zone of faulted structures may be further 

 defined as follows: 



1. The North-trending Group. This group in 

 Southern California includes the great Gulf of Cali- 

 fornia (Colorado) Depression, which follows the east 

 side and trend of the Peninsular Highlands. The 

 group is related to the Basin Range trend, which 

 lies in line with it to the north, but which is separated 

 from it by the "Transverse Belt." 



2. The first or Coast Range Group of northwest- 

 erly faults. This is represented by the trends of 

 the Coast Ranges of Northern California and the par- 

 tially submerged Catahna trends of the Continental 

 Shelf. Its direction is about north 40° west. 



3. The Northeast-trending Faults. The Tehachapi 

 (Garlock) fault is a conspicuous example of this group. 

 Although not so conspicuous in the structure pattern 

 of the region as are some of the other trends men- 

 tioned, other northeasterly trends significantly occur 

 in several localities of Southern California, as will be 

 further described. 



4. The Transverse or East-west-trending Group. 

 It consists of master faults and folds which accom- 

 pany the Great Transverse Belt. In this category is 

 included the anomalous group of curved faults and 

 folds elsewhere described under the head of the Ven- 

 tura Flexured Ranges. 



