2 (lEOLUGY OF THE EUEEKA DISTIIU'T. 



from the bold escarpment of the Sierra Nevada of (.'aliforuia to tlie prerip- 

 itous wall of the Wasatch Mountains of Utah, the distance across tlie 

 widest part in an east and west line being about 425 miles. These ranges 

 form long, narrow mountain uplifts with sharply defined limits, rising with 

 more or less abruptness above* dreary intervals of desert. Their nearly 

 uniform trend and the remarkable parallelism of the lines of upheaval of the 

 older sedimentary ridges present the most marked feature of the region. 

 In width they seldom exceed 8 miles, but frequently extend in an unbroken 

 line for more than 100 miles in length, with serrated peaks and ridges rising 

 from 2,000 to 6,000 feet above adjacent valleys. For the most part they 

 possess a simple topographical structure and a simple drainage system. 

 They are characterized, more especially the lower ranges, by absence of 

 trees, and in many cases are nearly bare of all vegetation, presenting rough, 

 rugged slopes of naked rock. 



(3n the higher parts of the plateau the rang-es, reaching a greater alti- 

 tude, partake more of an Alpine or sub-Alpine character. Precipitation 

 of moisture is more abundant, as seen both in the more frequent rains of 

 sunnner and snows of winter. A greater ^n'ecipitation produces larger and 

 more frequent streams, and a continued moisture favors a varied vegeta- 

 tion — the spurs and ridges being more or less covered with a dwarted and 

 stunted forest growth, and the long slopes with nutritious grasses. 



These salient features distinguish the ranges of the Nevada plateau 

 from those of Lake Lahontan and Lake BonneAdlle Basins, which present a 

 more arid and desolate aspect. A striking feature of nearly all these ranges 

 is their isolated position, only a few of them presenting outlying spurs or 

 low lines of rolling foothills. Occasionally inferior ridges of sedimentary 

 beds stretch diagonally across vallevs from one range to another, com- 

 pletely shutting in the intermediate valley, and still more frequently out- 

 bursts of volcanic I'ocks in irregular flows serve to unite in confused masses 

 bodies of sedimentary formations otherwise distinct. 



Midway between the Sierra and the Wasatch stand the East Hum- 

 boldt Mountains, the most jirominent range in the Great Basin. They pre- 

 sent, not only by reason of the greater number of rugged and coimnanding 

 peaks, many of them attaining an elevation over 11,000 feet above sea 



