142 SOUTHERN CALIFORNIA GEOLOCiY 



THE EAST-WEST FAULTS OF SAN 

 GORGONIO PASS 



At least two very conspicuous, east-west master 

 faults pass through San Gorgonio Pass. These, in con- 

 junction with the San Andreas Rift, have been strong- 

 ly influential, not only in producing the physiography 

 of that gateway to Southern Cahfornia, but also the 

 conditions which attend the northern termination of 

 the Peninsular Highlands. 



A portion of the course of the northernmost of 

 these faults, which may be termed the Banning fault, 

 has been partially described by Francis Vaughan.^ 



This passes through the southern portion of the 

 foothill mesas north of Banning and Beaumont. Dur- 

 ing the summer of 1927 the writer, assisted by Mr. 

 John C. Hazzard, traced this fault farther westward 

 through Hog Mountain and concluded that its course 

 probably continued westward through Crystal Springs 

 Pass, three miles east of Redlands. Its still farther 

 western continuations, now largely buried beneath late 

 formations, may probably pass north of the outlying 

 hills of the Jurupa type, which occompany the north 

 termination of the Peninsula highlands, and the south 

 side of the Ontario Valley, near Riverside and Colton. 

 K so, this explains much concerning the abrupt north- 

 ward determination of the Peninsula highland in this 

 region. 



The definite continuation of this fault eastward 

 from the San Gorgonio Pass is lost beneath the sands 

 of the Coachella arm of the Colorado Desert, but there 

 is a suggestion in the topography that either it or 

 the Lawrence fault, or both, may be represented in 



•Geology of the San Beinarilino Mountains. University of California Press. 



