12 BULLETIN 54^ U. S. DEPAETMENT OF AGEICULTURE. 



bod}' to the north, the Humboldt-Carson in the center, and the 

 Walker to the south. The divide between the Truckee and the 

 Black Rock was the last of the greater divides to appear, and with 

 its emergence the basin assumed its present major divisions. The 

 total area tributary to Lake Lahontan during the period of greatest 

 expansion was 45,730 square miles. The investigations of Russell 

 have shown conclusively that the lake never overflowed, and conse- 

 quently all the salts received from this tremendous area must" be 

 still within it. There follows a brief description of the topography 

 of the present divisions of the basin. 



THE BLACK KOCK BASIN. 



The present Black Rock Basin occupies an area of 8,550 square miles, mainly in 

 Nevada, but with extensions into Oregon and California. Its sink, the Black Rock 

 Desert, lies in the great filled trough east and southeast of the Black Rock Mountains, 

 and, with its extensions south-westward in the Granite Creek, Smoke Creek, and Mud 

 Lake Deserts, covers an area of over 1,030 square miles. The main present tributary 

 is the Quinn River, which enters the Black Rock Desert at its northern extremity. 

 Though the waters of the Quinn River still reach the sink at high-water periods, the 

 stream now possesses scarcely a tithe of its fonner idgor, and its channel is much 

 choked with debris and contains many alkali flats caused by local evaporation. Other 

 streams which lead toward the .sink are either dry except for occasional floods, or lose 

 themselves immediately on entering the playa. Like other playas, the Black Rock 

 Desert is not exactly level, but in the absence of accurate surveys the position of its 

 lowest sink is not determinable. Probably it contains several local depressions each 

 a few feet below the general surface and each separated from its neighbors by gentle 

 elopes and in"sdsible di\ades. After seasons of heavy snow and rainfall, shallow 

 bodies of water sometimes stand for several weeks in certain portions of the playa, 

 and these are probably among the areas of gieatest depression. 



From the mountainous country west of the Black Rock Mountains the basin receives 

 the overflow of High Rock Lake, with a drainage area of 670 square miles, and of 

 Summit Lake, which drains about 40 square miles. Water supply to both these 

 lakes is now so far reduced that their overflow, if any, seldom reaches the desert, but 

 essentially they still drain thereto and their drainage areas are included in the area 

 given above. 



During the higher stages of Lahontan the Black Rock section of the lake was 

 connected with or received the drainage from the Kumiva, Granite Springs, Hot 

 Springs, and Jungo Basins. Including these, its Quaternary drainage area (includ- 

 ing the area covered by the lake) was 10,500 square miles. The Honey Lake Basin, 

 though long connected with the Black Rock, is discussed as a separate unit and is not 

 included in the area given above. 



THE KUMIVA BASIN. 



The Kumiva Basin lies in the small trough east of Kumiva Peak and separated by 

 low alluvial divides from both the Black Rock Desert and the Granite Spring Basin, 

 next to be described. The age of these divides is uncertain, but both were covered 

 by the waters of Lake Lahontan. The di\ade into the Black Rock Desert is a little 

 the lower, and it is probable that when the Lahontan waters were subsiding the drain- 

 age out of the Kumiva Basin was in this direction. Indeed, it is quite probable that 

 this di\'ide is recent and was formed by post-Lahontan alluviation. The lowest de- 

 pression of the Kumiva Basin contains a playa abo.ut.lO square miles in area, but 



