148 SOUTHERN CALIFORNIA GEOLOGY 



along the north side of the Orocopia Mountains, the 

 south end of McCoy Mountain and through the north 

 side of the Chuckwalla Mountains. For thirty miles 

 of its course south of the Eagle Mountains this sup- 

 posed rift follows a long, ribbon-like valley suggestive 

 of a graben trough. 



RELATIONS OF THE TRANSVERSE STRUCTURE 



OF CALIFORNIA TO THE GREATER 



TRANSVERSE BELT 



The east-west structure lines of Southern Cali- 

 fornia are only parts of the greater transverse struc- 

 ture zone which extends across the entire American 

 Continental Mediterranean regions, as I have pre- 

 viously described. The continuity of the belt in Cali- 

 fornia is cut across in several places by the paths of 

 the later northwest systems, notably at Los Angeles, 

 Cajon Pass and probably at a point near the Colorado 

 River. In places its continuity is buried beneath Plio- 

 cene and Pleistocene sediments. These facts testify 

 to the relative antiquity of origin of the system, 

 which was probably at least as far back as pre-Plio- 

 cene time. Renewed movement has taken place on 

 some stretches in Pleistocene time, especially along 

 the Santa Monica and Cucamonga sections. 



THE NORTHEASTERLY TRENDING BELT 

 OF FAULT LINES 



Northeasterly trending faults also occur in Southern 

 California, but with a few conspicuous exceptions such 

 as that of the Garlock fault, they are mostly of the "in- 

 terior" kind, and do not constitute topographic boun- 

 daries as do those of the other directions described. 

 The great Garlock fault of this direction is one of the 

 most conspicuous master lineaments of California. The 



