NEVADA PLATEAU. 471 



by the snows of the neighboring high peaks, or else arid alkaline plains, 

 containing, during the eariy spring, shallow pools, but dry during the 

 greater part of the year, and frequently covered with incrustations of various 

 salts. The composition of many of these salines will be found scattered 

 through this report when speaking of the locality where they are found. 



Although all these valleys are marked by the absence of any arbores- 

 cent growth, they are for the most part, unlike the Salt Lake Desert, covered 

 with some vegetation, either one or two species of grasses, or else a stunted 

 development of shrubs and bushes. They present a monotonous, dreary 

 aspect of a dull greenish-gray color, derived chiefly from the Artemisia 

 tridentatay which usually stretches across the wide expanse of the valley. 



In their geological aspect, they appear equall}?- monotonous, and a 

 description of one would, with but little variation, answer for the many. 

 They are almost entirely covered by Quaternary deposits, made up of both 

 coarse and fine detritus derived from the adjacent ranges, overlying and 

 concealing, over the greater part of the area, the fine, impalpable, arenaceous 

 clays and silts of the Lower Quatenary formation, which is usually only 

 observed in the lowest portions of the valleys, or along the banks of streams. 

 Rarely, between the higher ranges, do formations older than the Quater- 

 nary reach the surface, so regular are the upheavals of the older sedimentary 

 beds and so great the accumulations of the overlying detrital matter. 



Taken together, the ranges of the Nevada Plateau present many fea- 

 tures in common, especially as regards their topographical structure. As 

 already mentioned, their trend varies but little, showing, as compared mth 

 other mountain-systems in the world, aremarkable parallelism, over such wide 

 areas, in the lines of upheaval of the sedimentary ridges. This regularity of 

 structure would be still more apparent, even to the superficial observer, but 

 for the great outflows of Tertiary volcanic rocks, which, occurring along 

 the old lines of upheaval, have spread out in all directions, concealing the 

 older sedimentary strata. These ranges rise from 2,000 to 6,000 feet above 

 the level of the adjacent valleys, presenting a mildly-serrated ridge, with 

 culminating peaks every few miles. In width, they vary from 5 to 10 miles. 

 In their transverse drainage-systems, and in their broader forms of erosions, 

 making allowances for the differences in geological structure, they show 



