82 GEOLOGICAL OISTORY OF LAKE LAHONTAK 



The water reaching playa-lakes is commonly derived from the surfiice 

 drainage of the basins in whicli they occur; tlie hirger ones, however, are 

 suppHed by streams more or less permanent. The sediment contributed to 

 lakes of this description is commonly in a stnte of minute subdivision, and 

 when derived from the surrounding surface is rich in saline matter. When 

 evaporation takes place both the suspended and dissolved matter is deposited 

 and forms a peculiar light-colored saline clay, which, when desiccation is 

 complete, forms a smooth mud-plain, or playa. 



The mud-plains originating in the manner described above are char- 

 acterized by the evenness of their surfaces and their light creamy-yellow 

 color, which is independent of the nature of the surrounding rocks. • These 

 deposits have the same characteristics and apparently about the same com- 

 position whether surrounded by sedimentary rhyolites or basaltic rocks. 

 In area they vary from a fraction of an acre up to many square miles. 

 They are entirely destitute of vegetation, and are in fact the only absolute 

 deserts in this country. During the rainy season they are rendered soft 

 and im[)assable, and very frequently covered with water, as mentioned in 

 describing a playa-lake, but with the advance of summer they lose their 

 moisture and become so completely desiccated beneath the intense heat of 

 the summer's sun that they resemble a pavement of cream-colored marble, 

 wdiich, on the broader deserts, stretches away to the horizon without a shrub 

 or spear of grass to break the monotony of the glossy surface. Owing to 

 the contraction of the mud on drying a playa becomes broken by a vast 

 system of intersecting "sun cracks," which frequently cover the surface with 

 an intricate network of narrow fissures. While the mud is soft it sometimes 

 becomes impressed with the foot-prints of animals and rippled by the winds, 

 thus receiving markings that are usually considered characteristic of shores. 



Typical examples of playas of broad extent occur in the Lahontan 

 basin, on the Black Rock, Smoke Creek, and Carson deserts; others of less 

 size are met with in various minor basins, as has been indicated in describ- 

 ing pla3'a-lakes. 



The scenery on the larger playas is peculiar, and usually desolate in 

 the extreme, but yet is not without its charms. In crossing these wastes 

 the traveler may ride for many miles over a perfectly level floor, with aa 



