Mountains of the South 223 



Santa Monica ranges are subordinate ridges or groups of hills, 

 as the Repetto and Puente Hills, Montebello Mountain, the 

 Newport-Inglewood fold, the San Juan Hills, the San Jose Hills, 

 the Jurupa Mountains, the Bunker Hill Dike, Box Springs 

 Mountains, and the Badlands of San Timoteo Canyon. 



The cores of all the mountain ranges are granitic in char- 

 acter, igneous rocks and metamorphosed sedimentary forma- 

 tions, the latter originally sandstones, shales, and limestones, 

 metamorphosed out of all semblance to their former characters 

 to quartzites, slates, schists, and marbles. The entire region is 

 cut and broken by faults. Igneous and metamorphic rocks 

 make up the greater part of the formations exposed at the sur- 

 face. All geologic sedimentary formations later than Jurassic 

 occur in larger or smaller areas, showing that portions at least 

 of the region were covered by the sea during the later geologic 

 ages. On the western slope of the Santa Ana Range an almost 

 complete series of geologic formations occurs, representing the 

 periods from early Cretaceous to Quaternary (and Recent) 

 time. 



Even a brief consideration of these mountain ranges, their 

 history and the processes by which they have come to their 

 present forms, would make a large volume. Only an outline 

 of the history and the agencies that have been involved will be 

 here undertaken. It will be convenient to begin with a con- 

 sideration of the Peninsular Range, taking up in brief outline 

 the Santa Ana, the San Jacinto, the Santa Rosa, the San Ber- 

 nardino, the San Gabriel, and the Santa Monica ranges, and 

 touching a few of the intervening regions which are closely 

 related to the adjacent mountains. 



The Peninsular Range a Great Elevated 

 Plateau 



The Peninsular Range of Southern California is essentially 

 a great uplifted plateau, cut off from the great Colorado Desert 

 valley on the east by a fault zone, uplifted more toward the 



