GENERAL CONCLUSIONS 241 



are recent, as is shown by the fact of their expression in the topography 

 and by their cutting the basalts, which are probably early Pleistocene.* 



General Conclusions as to Origin of Basin Ranges of Nevada 



AND California 



The process of mountain-building in this region has been compli- 

 cated, so it is to be expected that when the details shall have been more 

 closely studied many types of ranges will be found. But at present we 

 can hardly distinguish more than two — those formed chiefly by erosion 

 and those due directly to deformation. To the first class seem to belong 

 most of the mountains of the region. To the second class probably 

 belong part of the ranges of two outlying provinces — that which lies 

 between the southwestern boundary of Nevada and the Sierra Nevada 

 and that which lies near the Colorado river and separates the Colorado 

 plateau from the Basin region. 



In the region where the relief is due primarily to erosion there are 

 undoubtedly topographic features caused by direct deformation, which 

 in this case is comparatively recent and is of much less importance 

 than the older rock movements which erosion has overcome. 



Faulting in general seems to be about as frequent as in other regions 

 which show a similar amount of folding. The chief faults belong to a 

 north-and-south and an east-and-west system. There are also diagonal 

 ones running northeast and northwest, and in each of these systems they 

 may have a very great displacement. In mining districts like Hamil- 

 ton, Pioche, and Eureka there are many intersecting faults. This local 

 complexity is connected with vulcanism and ore deposition, and the 

 districts are the equivalents of Leadville and Aspen, in the Rocky 

 mountains. Even here the faults generally have no primary effect upon 

 the topography, as has been shown in the case of Eureka and Pioche, 

 while at Hamilton simple fault-scarps, due directly to displacement, are 

 probably present. This difference in the influence of faults on the to- 

 pography, which is chiefly dependent upon their relative age, is similar 

 to that in the Aspen district, where there is a complex of faults that 

 developed slowly and at different periods, so that only the most recent 

 have displaced the present surface.f In Meadow Valley canyon, south 

 from Pioche, a few of the post-Pliocene faults are accompanied by a cor- 

 responding surface displacement, but generally erosion has erased their 



♦ Dutton : Op. cit., pp. 118, 124, 125, 134. 



See also J. E. Spurr : Succession and Relation of Lavas in Great Basin Region. Jour, Geol. 

 vol. viii, no. 7, p. 636. 

 t Monograph xxx, U. S. Geol. Survey. 



XXXV— Bull. Geol. Soc. Am., Vol. 12, 1900 



