470 DESCEIPTIVE GEOLOGY. 



SECTION I. 



IBET^PAH MOUNTAINS TO RUBY VALLEY. 



BY S. F. EMMONS. 



To the west of the Great Desert is a region of high naiTow mount- 

 ain-ridges, with a general trend of north and south, or else invariably a 

 few degrees east of north and west of south. They are separated by 

 broad, nearly level valleys, which present, but in a less pronounced man- 

 ner, most of the arid desolate features of the Great Desert itself. These 

 longitudinal valleys are, however, as compared with the Desert of Utah, 

 relatively narrow, averaging, with a few marked exceptions, in general not 

 more than 10 to 16 miles in width, but occupying a considerably higher 

 level. Their elevation above the sea gradually increases to the west- 

 ward from that of less than 4,300 feet of the Great Desert to over 6,000 

 feet, measured at the lowest point in the valleys near the centre of the 

 region represented on Map IV. Of these valleys, Euby Valley, along the 

 east base of the Humboldt Range, is among the most elevated, retaining 

 its high altitude for a distance of over 60 miles. From the desert westward, 

 the mountain-ranges also increase in height and importance as far as the 

 East Humboldt Range, a lofty mountain mass occupying the middle of the 

 Nevada Plateau. This range now represents approximately the eastern 

 boundary of all the westward-running waters of the Nevada Basin. To the 

 west of this range, the valleys fall away gradually in altitude until, at the 

 lowest levels of the Nevada Basin, they lie between 300 and 400 feet below 

 the level of the Great Desert. The valleys west of the Humboldt Range 

 contribute to the transverse drainage-system of the Humboldt River, their 

 surfaces sloping upward from the river, both to the north and south, toward 

 the east and west systems of divide, which correspond roughly with the 

 north and south limits of the western half of the map. Many of the val- 

 leys, but more especially those east of the Humboldt Range, are -regions of 

 enclosed depressions, having no present outlet. In the bottoms of nearly 

 every valley are either small lakes of fresh or slightly brackish water, fed 



