130 SOUTHERN CALIFORNIA GEOLOGY 



5. The Second Group of Northwesterly Trends. 

 This occurs in Cahfornia in the wide territory between 

 the Colorado River at Blythe and the Pacific Ocean 

 at San Diego. It is also found in Southwest Arizona 

 and adjacent Mexico. It is a large belt of master 

 fault lines, about which more will be said later. 



The order in which the belts are given is a tenta- 

 tive approximation of their age sequence, which will 

 undoubtedly be modified and adjusted by researches 

 in the future. 



THE NORTH-SOUTH TRENDING BELTS 

 OF FAULTING 



Practically the whole of Eastern California north 

 of the Transverse Belt consists of a series of north- 

 south trending ranges and valleys, which owe their 

 position and grosser outlines to a series of faults of 

 similar direction. This is the western part of the Great 

 Basin Region of California, Nevada and Utah, The 

 Colorado Depression may have been synchronous with 

 this group in time of origin, which was early, or pre- 

 Miocene. 



The Sierra Nevada Highland is bordered on the 

 east side by a gigantic, northerly fault scarp, and it is 

 practically a cuesta-like fault block, the summit of 

 which slopes to the west-lying Great Valley. The 

 fault trends slightly more to the north-westerly than 

 the belt of north-south faults and rifts of the Great 

 Basin Region. 



The careful analyst of the topography in the field, 

 as delineated upon the maps, will observe north- 

 south, fault-scarp lineaments along the east front of 

 the San Bernardino and San Jacinto highlands, along 

 the course of Whitewater Creek at Palm Springs and 



