1912] 



Baker: Western El Paso Range 



137 



THE SOUTHERN SIERRA NEVADA 



The south front of the Sierra Nevada from Jawbone Canon 

 northeastward to Indian Wells is in a stage of physiographic 

 development older than that found in the range to the east and 

 west. This is due to a deformational history of this section of 

 the Sierra flank different from that of the greater part of the 

 range to the east and west. 



The Ricardo Erosion Surface 



From the summits above Walker Pass one looks out to the 

 east, north, and west over broad-topped summit mountains. 

 These broad summits have a gently rolling topography mani- 

 festly the product of an older erosion cycle than that which 

 formed the valleys which have isolated these peaks one from the 

 other. This old erosion surface is apparently, although not 

 certainly, the same as that of the Chagoopa Plateau described 

 by Lawson in the Upper Kern Basin. 9 What relation does this 

 old erosion surface bear to the peneplain of the Mohave Desert? 

 In order to determine this relation let us consider the region 

 lying between the crests of the Sierra and the peneplain developed 

 on the Rosamond series north of the El Paso Range. 



Above the piedmont alluvial aprons the peaks of the southern 

 Sierra rise rather abruptly. The lower slopes are rounded, while 

 back towards the summits the declivities are rugged and abrupt. 

 Long narrow shoulders run out into the desert with gradually 

 diminishing height. Between these shoulders are broad re- 

 entrants occupied by broad, mature, rather low grade, and open 

 valleys, in topographic conformity with the lower debris slopes, 

 and reaching far back into the range. It becomes at once evident 

 that we have here a topography which has already gotten beyond 

 the most rugged stage of maturity and is near early old age in 

 its development. This advanced stage of topography is only 

 found along the southern slopes; for in rising to the heads of 



o The Geomorphogeny of the Upper Kern River Basin, Univ. Calif. Publ 

 Bull. Dept. Geol., vol. 3, pp. 291-376, 1904. 



