SCIENTIFIC BACKGROUND 131 



other localities. These, although not continuous with 

 the main Sierra Nevada fault, are of similar direction 

 and somewhat in line with it. 



Collectively, the north-south structures are broadly 

 reflected in both the Great Basin and in the Colorado 

 Desert Regions of California, although the continuity 

 between them is now interrupted by the later-made 

 features of the Transverse Belt. 



These analagous lineaments, north-south high- 

 lands and depressions on either side of the Transverse 

 Belt may or may not represent vestiges of a once 

 continuous, north-south structural-zone vrhich was 

 broken across by the later development of the east- 

 west structures of the Transverse Belt and revived 

 along the path of the Whitewater, Palm Springs and, 

 perhaps, as yet undiscovered, faults of the San Ber- 

 nardino and San Jacinto Mountains. 



THE COLORADO DEPRESSION 



Although one cannot as yet produce much strati- 

 graphic evidence of the fact, one cannot avoid the 

 conclusion that the Colorado Depression, which is but 

 the northern end in California of the Gulf of Califor- 

 nia, is a structural trough. This lies between the 

 highlands of the Peninsular Ranges on the west and 

 the Southern Arizona and Sonora regions on the east. 

 Its northern end is abruptly terminated by a fault 

 escarpment w^hich accompanies the south side of the 

 highlands of the Transverse and Northwest Belts. 

 Abundant evidences are found of the uplift of the 

 highlands along the fault lines to the north side of the 

 depression, a notable instance being seen along the 

 highway through the Mecca Hills between Mecca and 



