16 BULLETIN 54, U. S. DEPARTMENT OP AGRICULTURE. 



but a divide over 200 feet high intervenes. This divide is probably pre-Lahontan 

 and the Allen Springs Basin has probably always been landlocked, except when Lake 

 Lahontan was high enough to overflow the divide. Previous connection with the 

 larger lake is sufficient to destroy the probability of a large amount of salt having 

 been accumulated or retained. The present area of the basin is 235 square milea 

 and that of the pi ya which occupies its present depressions is 4 square miles. 



THE SAND SPRINGS BASIN. 



From its southeast side an arm of the Carson playa stretches into the Sand Springs 

 Valley and is cut off from the main playa by a low and inconspicuous divide which, 

 according to Russell, is due to a small recent fault which cuts across the mouth of the 

 valley. . East of this the surface drainage of the valley has collected in a central 

 depression and deposited there a considerable quantity of common salt derived from 

 the more or less saline clays which floor this part of the playa. This deposit is entirely 

 recent and secondarj^, and there is no reason to suspect salt accumulations of impor- 

 tance to the present inquiry. In earlier times the Sand Springs Valley was filled 

 by Lake Lahontan, and even the fault-formed divide which now exists is apparently 

 quite recent. The drainage area cut off by this divide aggregates 200 square miles. 



Just south of the Sand Springs Valley there is another arm of the main playa, also 

 containing an alkali flat and a salt deposit, and probably possessing a similar topog- 

 raphy and structure. These are not known in detail to the writer and the valley has 

 been included with the Humboldt-Carson in all computations. 



THE BUENA VISTA BASIN. 



Turning now from those cut-off valleys previously tributary to the main Carson 

 water body to those' tributary to the Humboldt River, the'first basin to engage atten- 

 tion is the Buena Vista. This occupies the trough extending northeastward and 

 lying between the Humboldt and East Ranges. Toward the south the basin is barred 

 from the Carson playa only by a low divide, and a similar low divide separates it from 

 the Humboldt River to the north. The latter divide is apparently the lower and is 

 alluvial, whereas King maps the southern divide as of basalt. Both divides were 

 overtopped by the waters of Lahontan, but the southern was probably the earlier 

 exposed and in the latest Lahontan stages the Buena Vista Valley was probably a 

 tributary of the Humboldt River. The present bottom of the valley is occupied by a 

 playa of the usual character and with an area of about 50 square miles. The total area 

 of the present basin is about 4,000 square miles, but this area is somewhat uncertain, 

 because the position of the alluvial divide at the northern end is not exactly known. 



THE BUFFALO SPRINGS BASIN. 



The Buffalo Springs Basin is a small valley lying north of the Battle Mountain 

 range and separated from the Reese River only by a low divide composed partly of 

 alluvium and partly of blown sand. This divide appears to be very recent and there 

 can be little question that the time is short since the drainage of the basin found free 

 egress to the Reese River and thence to the Humboldt. The area of the basin is 

 about 500 square miles, there being again some uncertainty as to the exact position of 

 the recent divide. It contains a playa approximately 25 square miles in area. 



THE CRESCENT VALLEY REGION. 



East of the north-south trough occupied and drained by the Reese River and extend- 

 ing eastward as far as the Sulphur Springs Range is an area of rather complicated 

 topography in which the north-south trend of valleys and ranges, while still traceable, 

 becomes less obvious. This area has been very inadequately mapped, and the infor- 



