DESERTS OF THE GREAT BASIN. 9 



The valleys or plains separating the mountain ranges, far from being 

 fruitful, shady vales, with life-giving streams, are often absolute deserts, 

 totally destitute of water, and treeless for many days' journey, the gray- 

 green sagebrush alone giving character to the landscape. Many of them 

 have playas in their lowest depressions — simple mud plains left by the evap- 

 oration of former lakes — that are sometimes of vast extent In the desert 

 bordering Great Salt Lake on the Avest and in the Black Rock Desert of 

 northern Nevada are tracts hundreds of square miles in area showing 

 scarcely a trace of vegetation. In winter, portions of these areas are occu- 

 pied by shallow lakes, but during the summer months they become so baked 

 and hardened as scarcely to receive an impression from a horse's hoof, 

 and so sun- cracked as to resemble tessellated pavements of cream -colored 

 mai'ble. Other portions of the valleys become incrusted to the depth of 

 sev.eral inches with alkaline salts which rise to the surface as an efflores- 

 cence and give the appearance of drifting snow. The dry surface material 

 of the deserts is sometimes blown about by the wind, saturating the air 

 with alkaline particles, or is caught up by whirlwinds and carried to a great 

 height, forming hollow columns of dust. These swaying and bending col- 

 umns, often two or three thousand feet high, rising from the plains like pil- 

 lars of smoke, form a characteristic feature of the deserts. 



Most of the rivers of the Great Basin have their sources in the melting 

 snows of the mountains which form its eastern and western borders, and 

 flow into the desert valleys within the rim of the undrained area. Of such 

 the Bear, Weber, and Sevier rivers are examples along the eastern border; 

 on the west the Truckee, Carson, and Walker rivers have a similar origin 

 and destinjr. A single river, the Ilumboldt, is anomalous in that both its 

 source and its terminus are well within the area of interior drainage. 



The rivers of the Great Basin vary greatly in volume with the varying 

 seasons, and some of them disappear entirely during the hot summer months 

 In the streams that are perennial a high percentage of the annual discharge 

 is crowded into a brief space toward the end of the rainy season. Thus 

 the arteries of this parched and heated country make but one feverish pul- 

 sation in a year. The streams usually diminish in volume as they descend 

 into the valleys, and in many instances their waters are lost on the thirsty 



