1912] 



Baker: Western El Paso Range 



135 



subsequent courses in a region of lower altitude and less resistant 

 rocks. The lower narrows cannot be consequent to the original 

 slope formed by the uplift. They cannot be superimposed 

 because the El Paso Range and the adjoining Kane basin are 

 structural features which do not owe their larger orographic 

 features to erosion. Hence they must be either antecedent in 

 their origin or have cut back through the range by headward 

 erosion and captured and diverted drainages more nearly con- 

 sequent to the uplift- 

 There are several facts against the view of the development 

 of these lower canons by headward erosion. All the other drain- 

 age courses on the south side of the range are small and have 

 cut back but a short distance into the mountain ridge. Their 

 valleys have steep gradients out of topographic adjustment with 

 the Kane basin to which they are tributary, but the valleys of 

 Red Rock Canon and Last Chance Gulch are in topographic 

 adjustment with the basin. Red Rock Canon and Last Chance 

 Gulch have valleys which are no older in their lower courses just 

 inside the southern scarp than where they first enter the more 

 resistant rocks farther up. No evidence of the former existence 

 of a consequent drainage down the northern flank of the range 

 and around its western end into the Kane basin or eastward into 

 the Salt Wells Valley was found, although these regions were 

 not fully examined in the field. It is apparently hard to account 

 for the devious windings of the narrow but deeply incised Last 

 Chance Gulch, cut in aparently homogeneous granite, if its course 

 was developed by headward erosion, but these meanders may 

 very well have been inherited from a previous cycle. Also the 

 drainage channels of the north flank, developed along the strike 

 of the Rosamond strata, do not follow the foot of the range, but 

 have become subsequent. They have shifted their courses until 

 the broadest, largest, and deepest of them have come to occupy 

 the contact between the Rosamond series and the more resistant 

 basement complex in the manner first explained by Gilbert in 

 his account of the geology of the Henry Mountains of Utah. 

 The fairly well adjusted drainage of the north flank is in marked 

 contrast with the canons cutting through the range. Finally, 

 no evidence is known of lower gaps in the profile of the range's 



