RANGES OF WESTERN CENTRAL NEVADA 231 



that tlie ran.uH^ is directly duo to deformation, is in this case rather au 

 evidence of deep erosion. 



Walker Ixirer range.— As the Walker River range is chiefly composed 

 of i^nieous rocks, it is difficult to draw such reliable conclusions as to its 

 structure and origin as in the case of the range made up of stratified 

 rocks. This range on its eastern side has a steep scarp, resembling in 

 miniature the eastern scarp of the Sierras. At the foot of this is Walker 

 lake. The scarp has been explained by Professor Russell as having been 

 formed directly * by a fault. We are, however, without convincing evi- 

 dence as to whether the scarp is a simple erosion scarp, a simple fault- 

 scarp, or an erosion fault-scarp (the latter term signifying a scarp formed 

 by erosion along a fault-plane), for in the first i)lace we have no proof 

 of the fault's existence, and in the second place, supposing the fault to 

 exist, we have no proof of its relation to the origin of the scarp. On the 

 other hand, the basal erosion at the foot of the scarp is strongly marked. 

 As has been stated. Walker lake and Walker river lie here, and in former 

 times the lake was more extensive, being an arm of the greater lake 

 Lahontan. The erosive action of the present lake is probably not in- 

 considerable, and that of the ancient lake is abundantly proved by the 

 high and deep terraces, which are at least several hundred feet high and 

 1 or 2 miles in width, and are composed of great angular and subangular 

 boulders derived from the mountain above. The abstraction of so much 

 material from the base of the mountains would have perhaps formed 

 the scarp without any other agency. 



Pinenut and Virginia ranges a,nd the eastern face of the Sierras. — What 

 has been said concerning the Walker River range applies also to these 

 ranges, which have similar characteristics. They are chiefiy made up of 

 igneous rocks, and show abrupt east-facing scarps, while the west face is 

 generally but not alwaj^s of gentler slope In each range also the steep 

 eastern side is composed chiefly of granular rocks, while the western 

 side is typically covered by volcanics. This of itself is not a clue to the 

 origin of the mountains, for such would be the case whether the scarp 

 was formed by erosion or by faulting. There are, however, evidences of 

 north-and-south lines of fracture, which are very likely also lines of dis- 

 placement. Springs break out along these, from which it happens that 

 they are also lines of erosion, producing within the ranges longitudinal 

 gulches. It is very likely that the steep eastern scarps are marked by 

 similar displacements, which may be greater than ordinary. On account 

 of the considerable erosion which is shown throughout this district, 



however, it seems more probable that the mountain fronts are not simple 



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♦Monograph xi, U. S. Geol. Survey 



