446 A NATIONAL PLAN FOB AMERICAN FORESTRY 



mountain chains. Another part of the water supply comes from 

 large springs at lower elevations or from underground storage basins 

 fed principally from forest-covered mountain slopes. The main irri- 

 gation developments depend upon large streams, but numerous small 

 streams furnish the water necessary to irrigate a large number of 

 widely scattered farms and ranches. 



In the Sierra Nevada the principal coniferous timber types are the 

 ponderosa pine at the lower elevations and a mixture of white fir, 

 incense cedar, Douglas fir, and sugar pine at somewhat higher eleva- 

 tions. Still higher Jeffrey pine and western white pine come in, ulti- 

 mately blending into the subalpine forest. In the eastern part of the 

 basin the coniferous timber type is made up mainly of Douglas fir, 

 alpine fir, and white fir, with some spruce. The aspen-fir-brush type 

 is characterized chiefly by extensive aspen stands and by mixed 

 stands of aspen, fir, and brush. It occurs principally in the eastern 

 portion of the basin, on mountains and plateaus above elevations of 

 7,500 or 8,000 feet. 



Both the coniferous and aspen-fir-brush types normally form a 

 moderately dense cover of trees and subordinate vegetation, have a 

 fair to good litter cover, and produce a rather deep layer of humus. 

 Precipitation within these types is probably 20 inches or more in 

 nearly all parts of the basin, and in some localities exceeds 40 inches. 

 Much of this precipitation comes in the form of snow, which tends to 

 accumulate, especially at the higher elevations. Rising temperatures 

 in March, April, and May and occasional warm rains at that time 

 cause rather rapid melting. The chief watershed-protective value of 

 these types lies in maintaining a surface soil condition favorable to 

 percolation of moisture from melting snow and rams, in retarding 

 snow melt and surface run-off, and in checking erosion. 



Water for domestic use, power, and other urban purposes, also, 

 comes mainly from forest areas. Such important cities as Salt Lake 

 City and Ogden, and more than 130 other communities having a pop- 

 ulation of 500 or more, obtain their supplies from these watersheds. 

 Several rather large power developments have been installed on the 

 mam rivers to supply cities and large towns and in portions of Utah 

 and Idaho included in this basin many towns have their own power 

 plants on nearby streams. 



FLOODS 



Of almost equal importance with adequate water supply is the con- 

 trol of local floods, which are destructive chiefly because of the exces- 

 sive load of soil and rocks which they carry. Floods of greater or less 

 seriousness have been reported from many areas within the Great 

 Basin in the last 30 to 50 years, especially following destruction of 

 cover on the watersheds through the excessive grazing which came 

 with extended white settlement and through fires and heavy timber 

 cutting. Some of the most destructive floods have occurred in the 

 last 10 years in the thickly populated area near Salt Lake. 



Studies made by Prof. Reed W. Bailey, 73 of the Utah Agricultural 

 College, in cooperation with the Intermountain Forest and Range 

 Experiment Station and the Utah State Land Board, have shown 

 that the 75-foot or deeper channel cutting and the enormous amounts 



73 Bailey, Reed W., statement in hearings before the House Committee on the Public Lands on H.R. 

 11816, 72d Cong., 1st sess. 1932. 



