224 
GREAT BASIN PROBLEMS 
by numerous short and relatively low mountain ranges, of a gen^ 
eral north and south trend, which divide the region into valleys 
with floors from 4000 feet to 5000 feet above sealevel. There are 
occasional deeper depressions; and there are many small mountain 
valleys at considerable altitudes. The mountain peaks of the re¬ 
gion sometimes reach an altitude of 12,000 feet. The waters have 
cut deep canyons, through which the rivers enter the valleys and 
are lost in “sinks” and shallow lakes. 
In Pleistocene days two great lakes filled a large part of the 
Great Basin area; Lake Bonneville in the east, in the Utah part 
of the basin; and Lake Lahontan to the west, in the western Ne¬ 
vada portion. Numerous smaller lakes filled other depressions. 
We are at this moment on the Provo level of Lake Bonneville. At 
one time the waters of Lake Bonneville were several hundred feet 
above this level. These great bodies of ancient waters have shrunk 
to relatively small salt lakes, the best known of which is the Great 
Salt Lake. 
The Sierra Nevada intercepts and condenses the moisture that 
would otherwise fall upon the Great Basin. Consequently the val¬ 
leys of the Great Basin are among the most arid in North America. 
The precipitation comes chiefly in late winter and early spring; 
the summers are almost rainless except in the southern part, where 
the Arizona type of precipitation prevails. The annual rainfall in 
the valleys varies from less than two inches to 18 or 20 inches. 
The average for the valleys is probably not above 10 inches annu¬ 
ally. In the mountains, however, the rainfall is much heavier 
sometimes reaching thirty-five or forty inches annually. The 
relative humidity is very low, causing rapid evaporation 
of all moisture. The annual temperature is not greatly differ¬ 
ent from the average of the United States; but the daily range, 
due to the clear skies, thin air and scanty vegetation, is much 
greater. Snow falls upon most of the Great Basin, but seldom 
lies long on the ground. The Great Basin is a land of almost con¬ 
stant sunshine, clear skies, dry atmosphere, comfortable summers 
and easy winters. 
Into this desert area settlers have been moving since 1847. Won¬ 
derful conquests of nature have been achieved. Yet, the popula¬ 
tion of the Great Basin does not exceed four or five persons per 
square mile. It is today essentially an unconquered country. The 
