‘TOPOGRAPHIC FEATURES OF THE DESERT BASINS. 14 
This classification, while setting out to be both genetic and geo- 
graphic, has ended by being scarcely more than arbitrary, but this 
seems not to be remedied, and it is hoped that the index and the key 
map will help to cover the lack of a more logical arrangement. Each 
basin or group of basins has been given a name by which it is known 
throughout the report and which is, wherever possible, the name by 
which it is known to residents of the neighborhood or in former 
geologic studies. These names are given on the accompanying 
map, in the index, and in the synoptic list of Table I (p. 60) and will 
enable the ready location of information concerning any basin or 
region. 
THE LAHONTAN BASIN AND ITS TRIBUTARIES. 
At the present time the Lahontan Basin contains internal divi- 
sions, structural and alluvial, dividing it into a number of separate 
basins of which the major are the Black Rock Basin, the Humboldt- 
Carson Basin, the Truckee or Pyramid Lake Basin, and the Walker 
Basin. The studies of Russell’ have shown that the water of Lake 
Lahontan rose sufficiently to unite all of these basins into one water 
body. At the highest stages of the lake the present Humboldt-Car- 
son Basin was connected with the Walker through the pass south of 
old Fort Churchill, with the Truckee through the Ragtown Pass 
and the pass at Wadsworth, and with the Black Rock through the 
pass north of Humboldt Station on the Southern Pacific Railway, 
the latter basin being also connected with the Truckee at the north 
end of the present Pyramid Lake. Both the Black Rock and 
the Truckee Basins were connected with the smaller Honey Lake 
Basin through passes at the northwest corner of the present Pyramid 
Lake. At this time the drainage area of the Humboldt River was 
much greater than at present, a large part of it having since been 
cut off by alluvial damming. The areas tributary to the Truckee 
and Walker Rivers were also slightly larger than now. The Carson 
was practically the same. 
As the waters of the lake went down the first divide to appear 
was probably that between the Humboldt-Carson and the Allan 
Springs Basin, a small tributary to the south. Next the Walker 
became a separate basin, though perhaps contimuing to overflow 
into the Humboldt-Carson. At about the same stage the direct 
connection between the Humboldt-Carson and the Black Rock 
was broken, though there still remained the indirect connection 
through the Truckee. A hundred feet additional lowering saw the 
appearance of the divide at Wadsworth between the Humboldt- 
Carson and the Truckee and the separation of the original lake into 
three water bodies—the Black Rock, Honey Lake, and Truckee 
1U. 8S. Geological Survey, Monog. XI (1885). 
