TOPOGRAPHIC FEATURES OF THE DESERT BASINS. 15 
In its upper courses the Carson River, like the Truckee, has kept some measure of 
its vigor and retains essentially its Lahontan drainage. Farther down, where it flows 
over what was once its flood plain at, the margin of the retreating lake, it has leit many 
local playas which are now without escape for their waters. All these were either 
covered by Lake Lahontan or were tributary to it, and have no importance in the 
present connection. 
The history of the Humboldt River is very different. More than any other river 
of the Great Basin, perhaps excepting the Mojave, it has suffered by alluvial damming 
and by the decay ofits tributaries. Its present drainage area is scarcely a half of that 
which it once possessed. The description of the Humboldt in detail is unnecessary. 
In general it may be said that it cuts across the northern extremities of the trough 
valleys in the eastern half of the Lahontan area, draining these valleys north as far 
as the limits of the Great Basin and south to the alluvial divides which separate the 
Lahontan drainage from that of the Colorado River and of the smaller basins to the 
south. Several of these trough valleys, once tributary to the Humboldt, have been 
cut off behind alluvial dams, creating the Buena Vista, Buffalo Springs, Crescent 
Valley, Gibson, and Clover Basins. Even where the valleys have not been cut off 
entirely, the decay of the streams has left them with innumerable local playas and 
alkali flats but since these are still essentially tributary to the Humboldt they do not 
require individual discussion. 
The Humboldt and the Carson are the only important rivers tributary to the basin. 
A few small valleys tributary to, or filled by, the Great Lake are discussed below 
as the Fernley, Allen Springs, and Sand Springs Basins. The present drainage area 
of the Humboldt-Carson, including all local playas and other areas not cut off by actual 
divides, is 19,300 square miles. Its Quaternary area was 27,575 square miles. 
Mention should perhaps be made of the Ragtown Soda Lakes, situated on the Carson 
Playa, about 6 miles northwest of Fallon. These are small depressions, probably of 
volcanic origin, in the bottoms of which are lakes of brine from which carbonate of 
soda was once made commercially. From his studies of the lakes Russell concluded 
that their soda content was probably derived from waters which had percolated 
through the saline clays of the surrounding playas and acquired salinity therefrom. 
They are not believed to have any important significance to the present inquiry. 
The Wabuska topographic sheet of the United States Geological Survey shows 
another small local depression in the eastern extension of the Pine Nut Mountains 
about 4 miles east of Lyon Peak. Its nature is unknown to the writer, but it is too 
small to have any practical importance. 
THE FERNLEY BASW. 
The Fernley Basin is a small depression lying between the Humboldt-Carson and 
the Truckee Basins, as does the Jungo Basin, between the former and the Black 
Rock. When Lahontan was high this basin was a strait connecting these two water 
bodies. On the fall of the waters the connection with the Truckee was broken first, 
the connection with the Humboldt-Carson, by way of Ragtown Pass, remaining much 
longer intact. At the present time the bottom of the Fernley Basin is about 100 
feet below this pass, but it is not certain that this has always been so. Recent alluvial 
deposition must be taken into account and is difficult to estimate. The present bot- 
_tom of the basin carries three playas, the two extreme of which drain toward the 
central one. All the playas are somewhat saline, but no segregated salt deposits are 
known. The area of the present basin is 215 square miles. 
THE ALLEN SPRINGS BASIN. 
South of the Carson Playa there is a deep, narrow mountain valley which was filled 
by the Lahontan waters and connected with them through a narrow strait at Allen 
Springs. The bottom of this valley is about of the same level as the Carson Playa, 
