TOPOGEAPHIC FEATUEES OF THE DESEET BASINS, 15 



In its upper courses the Carson River, like the Truckee, has kept some measure of 

 ita 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 left 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 of its 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 

 aa 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 Femley, 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 fflnall 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 PERNLEY BASIN. 



The Femley 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 Femley 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 accoimt 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, 



