12 BULLETIN 54, U. S. DEPARTMENT OF AGRICULTURE. 
body 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 ROCK 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 southwestward 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 former vigor, and its channel is much 
choked with débris 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 
slopes and invisible divides. 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 greatest 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 divide 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 divide is recent and was formed by post-Lahontan alluviation. ‘The lowest de- 
pression of the Kumiva Basin contains a playa about 10 square miles in area, but 
