1922] Vaughan: Geology of San Bernardino Mountains 405 



In addition to the faulting there is another structural feature of 

 great importance, a general uplift or doming of the whole region. 

 The upper portion of the mountains, the pass on the south, and the 

 desert on the north all slope gently to the southeast. The Lion sand- 

 stone is of marine origin and not older than lower Pliocene, but it 

 now lies at an elevation of about 2000 feet. This merely proves that 

 the uplift is later than lower Pliocene, but other considerations indi- 

 cate that it is probably very recent. Such orogenic disturbances as 

 general uplift and faulting usually go together. The youthful nature 

 of the mountain mass shows that the faulting must be very recent and 

 therefore suggests that the general uplift of the region is also recent. 

 The divide in the San Gorgonio Pass is at Beaumont. To the west is 

 San Timoteo Canon, which has cut back until it taps the pass a mile 

 from the town. Several other canons have reached the pass from the 

 south in a similar manner. This cutting still continues with the 

 aggressiveness of youth, while if the uplift were of ancient date this 

 upper part of the pass would have been cleaned out. It therefore 

 seems probable that the general uplift of the region as well as the 

 faulting which has given rise to mountains must be recent, and, indeed, 

 it may still be under way. 



Summary. — The older sediments of the region have been folded 

 and faulted and then intruded by granitic rocks. The resulting struc- 

 ture has been further complicated by other granitic intrusions. In 

 Bear Valley, and immediately to the north and east, there are consid- 

 erable areas of the older sediments, some of which were probably roof 

 pendants. Farther east, on the Saddleroek plateau, the older granites 

 are found in such relationships to the younger as to suggest that they 

 formed a roof over the latter at the time these invaded the country. 

 South of Antelope Creek and Santa Ana Canon the structural rela- 

 tionships of the older rocks are too complicated for description. 



The unaltered Tertiary sediments along the south flank of the 

 mountains are considerably folded and faulted and dips as high as 

 70° are found. 



The San Bernardino Mountains owe their existence as such to a 

 great system of Quaternary faults, which also extends into the Mojave 

 Desert to the north. Most of these faults are evidenced by scarps, 

 some of which are rather imposing. On the north side of the moun- 

 tains a fault extends eastward from Silver Creek to Blackhawk Canon 

 and another from Blackhawk Canon southeastward to Rattlesnake 

 Canon. North of the latter a somewhat smaller fault, striking east- 



