Vol. 6] Baker: Cenozoic History of the Mohave Desert. 369 



Fault-Scarps. — The San Bernardino Range is bounded on the 

 south by a fault-scarp, along the base of which runs the San . 

 Andreas rift. 10 There is probably a fault-scarp along the north 

 base also. The scarps, which are considerably eroded, are about 

 equally steep ; the amount of upward movement on both the 

 faults has probably averaged about four thousand feet. The 

 San Gabriel Range, the Sierra Pelon, and Liebre and Sawmill 

 mountains, forming the southwest border of the Mohave Desert, 

 have a fault-scarp on their north bases. The southern front of 

 the Sierra Nevada east of Tehachapi Pass shows much topo- 

 graphic evidence of a recent fault-scarp. The base of the range 

 forms a straight line for miles ; triangular facets are evident 

 between the short, deep, narrow canons cutting back into the 

 mountain front ; the canons are not topographically adjusted 

 to the basin south of the mountain front ; and features which are 

 apparently caused by a physiographic rift between the bedrock 

 slope of the mountains and the debris apron were noted. The 

 scarp was last seen a mile or two west of Red Rock Canon, the 

 region farther east not being examined. 



Rejuvenation. — Active canon-cutting is in process along the 

 fault-scarps. The lower courses of the broad alluviated valleys 

 in the San Bernardino Mountains have become deep narrow 

 canons. Cottonwood Creek, which emerges from the south base 

 of the Tehachapi Mountains about twenty-five miles east of Tejon 

 Pass, has cut a series of three alluvial terraces, although not all 

 of this cutting may have been caused by recent uplift. The 

 citing of many other examples would only be unnecessary repeti- 

 tion. There is a patch of cemented gravel on the east wall of 

 Furnace Canon, and fifty feet above the present canon bed, 

 near where that canon leaves the north base of the San Ber- 

 nardino Range. Another gravel remnant was noted much higher 

 above the stream bed and higher up in the range on the dividing 

 ridge between Wild Rose and Furnace canons. Well-cemented 

 stream gravels containing placer gold and proboscidean bones 



is Mendenhall, W. C, The hydrology of San Bernardino valley, Cali- 

 fornia, U. S. Geol. Surv., W. S. and I, paper no. 142, pp. 30 and 31, 1905. 



Fairbanks, H. W., Report of the State Earthquake Investigation Com- 

 mittee upon the California Earthquake of April 18, 1906, Carn. Inst. 

 Publ., no. 87, vol. 1, pt. I, pp. 43-47, 1908. 



