SCIENTIFIC BACKGROUND 161 



viving after-effects of the greater movement along 

 it in Pleistocene time. 



THE SAN ANDREAS RIFT IN SAN GORGONIO 



PASS 



The course of the San Andreas Rift adjacent to and 

 along the southwest side of the San Bernardino Plateau 

 and through the San Bernardino Valley and San Gor- 

 gonio Pass is recorded by one of the most beautiful and 

 majestic fault scarps in California. This feature is 

 visible for forty miles between Cajon Pass and the 

 Colorado Desert and has many lovely towns and cities 

 nestled near its foot, including San Bernardino, Red- 

 lands, Beaumont and Banning. The escarpment rises 

 for more than a mile above the plain of the San Ber- 

 nardino valley at its southern base and to a nearly uni- 

 form skyline which is termed the "Rim of the World." 

 It is indeed a wonder feature, the beauty and ma- 

 jesty of which is enhanced by many subsidiary 

 features, such as secondary rift lines, talus fans, 

 faceted salients, terraces, cross-cutting river-canyons 

 and escarpment erosions, all of which will undoubtedly 

 some day be described in detail by others. 



This portion of the rift is not a single, simple fault 

 line, but is a more or less complicated zone of parallel 

 faults which not only attend the immediate base of 

 the escarpment, but are found in the valley below. Its 

 intricate details, we understand, are being worked out 

 by Mr. Noble, but his results are not available. 



The foot line of the scarp, which may be tentatively 

 considered the main rift, sends out several branches 

 as it approaches the San Gorgonio Pass and as it passes 

 through its north side. One of these is known as the 



