The Pleistocene Lake in Spring Valley, Nevada, and its climatic implications

The present-day climate of Spring Valley, Nevada, is compared with elements of the Pleistocene climate. The modern climate ranges from semiarid on the valley floor to subhumid in the mountains. Evaporation is estimated as about 44 inches per year. Under the prevailing conditions of precipitation and evaporation, Spring Valley does not have a lake. The Pleistocene lake had an area of 335 square miles which was 21 per cent of the 1630-square-mile drainage basin. According to the geologic evidence, Spring Valley was never filled to overflowing. A lake at the overflow level would have been nearly 250 feet deeper and would have had an area of 580 square miles, which is 36 per cent of the drainage basin. Studies of the hydrologic regimen that would be required to maintain a Pleistocene lake indicate that relatively small adjustments of evaporation and precipitation would be necessary. The most likely combination of adjustments among those possible suggests a 30 per cent decrease in evaporation rates and an 8-inch increase in precipitation.