546 0. E. MEINZER LAKES OF THE BASIN-AND-RANGE PROVINCE 



basins are of three types: (1) those in which lakes still exist, (2) those 

 which do not have lakes, but are discharging water from the subterranean 

 reservoirs into the atmosphere by evaporation and transpiration, often in 

 large quantities, and (3) those which do not have lakes and in which, 

 moreover, the water-table is everywhere so low that they do not discharge 

 ground-water except by subterranean leakage out of the basin. A basin 

 with ground-water discharge has a different aspect from one without such 

 discharge and it functions differently. Instead of being completely desic- 

 cated except in brief rainy seasons, as was the conception once usually 

 held, it may in fact contain a vast reservoir of ground water that is dis- 

 charging large quantities of water by evaporation and by transpiration 

 from plants throughout all the dry, hot, summer season, though no water 

 may be visible at the surface. Only a few of the basins at the present 

 time have perennial lakes that are discharging water by evaporation, but- 

 many of them have extensive areas of ground-water discharge. Data are 

 being accumulated for constructing a map of the areas of ground-water 

 discharge in the Basin-and-Eange Province. This map will probably 

 show that, excepting the basins of Lakes Bonneville and Lahontan, the 

 aggregate area at present discharging water by evaporation and transpi- 

 ration from ground-water reservoirs is not greatly inferior to the aggre- 

 gate area which in the Pleistocene was discharging by evaporation from 

 lakes. The north basin of Big Smoky Valley, Nevada, may serve to illus- 

 trate the importance of ground-water discharge (figure 3). In this basin 

 there is an area of 160 square miles in which ground water is being dis- 

 charged into the atmosphere. The average rate of discharge in this area 

 has been roughly estimated to be 6 inches of water a year, which would 

 amount to about 50,000 acre-feet a year, or 45 million gallons a day— 

 about 8 per cent of the water that falls on the basin as rain or snow. 



While the aggregate discharge of ground water is a very large quantity, 

 it should be noted that the rate of discharge is much lower than the rate 

 of evaporation from a lake under the same atmospheric conditions. If 

 the average annual evaporation from a free water surface in Big Smoky 

 Valley is 60 inches and the average annual rate of loss from the area of 

 ground-water discharge is only 6 inches, then the ground-water discharge 

 is equal to the evaporation from a lake of 16 square miles occupying l 1 /^ 

 per cent of the drainage basin. The Pleistocene lake in this basin occu- 

 pied 225 square miles, or 18 per cent of the basin (figure 4). The quan- 

 tity of water that would be discharged by evaporation from a lake of this 

 size under present climatic conditions would, according to the assump- 

 tions made, be about 14 times the present ground-water discharge and 



