122 SOUTHERN CALIFORNIA GEOLOGY 



has taken place in various geologic periods in the 

 Trans-Pecos region of Texas. The northeast, south- 

 west trends of Appalachian relationships (Marathon 

 ridges) are cut across by trends of north-south direc- 

 tions (Rio Grande ranges) probably of early Tertiary 

 (Rocky Mountain) age. Both of these are again 

 crossed by northwest trends of later Tertiary age and 

 Pacific relationships.^ 



At Los Angeles, older, northwest folds in the east 

 end of the Santa Monica Range are cut across by 

 east-west faults, and the latter are cut across by faults 

 of the Second Northwest system. Other instances of 

 crossings of the trends in Southern California can be 

 given. Nearly all of the larger mountain passes into 

 Southern California represent gaps along places where 

 there has been a meeting or a crossing of the trends. 



The crossing of the fault lines of one system by 

 those of another is notably observable on a large scale 

 in the outlines of the San Gabriel, San Bernardino, 

 San Jacinto and Peninsula Ranges. It is likewise ob- 

 servable in some of the other physiographic features 

 like the Perris peneplain, the Puente and San Pedro 

 Hills and the east end of the Santa Monica range, 

 where in each instance master fault lines of one direc- 

 tional system and of an earlier date are cut across 

 by master faults of another and later system. Noble 

 has noted how the Basin Range type of faults are cut 

 out by the Garlock fault. 



The northern part of the north-south trending Pen- 

 insula Highland is crossed diagonally from a northwest 

 to southeast direction by several master rifts of the 



'See Physiographic Atlas of the U. S. Geological Survey No. 3 by the 

 writer. Also see map by C. L. Baker which accompanies Bulletin 117 of the 

 University of Texas Bureau of Technology. 



