A NATIONAL PLAN FOR AMERICAN FORESTRY 425 



Nevada is narrow and steep. Only a very small part of that watershed 

 is covered by coniferous forest. A somewhat larger part of it is 

 woodland. The principal forest trees, whitebark pine, Jeffrey pine, 

 pinon, and juniper, grow in open stands and produce only small 

 quantities of litter, and there is seldom a dense cover of undergrowth. 

 Rainfall is light, ranging for the most part from 10 inches to 20 inches 

 or slightly more at the higher elevations. The granitic soil is rather 

 porous and ordinarily is not readily eroded. Because of these con- 

 ditions most of the forested area has been classed as of moderate and 

 some as of slight watershed-protective influence. The importance of 

 the water supply, however, may justify classifying part of this area 

 as of major influence. 



The forested areas at the southern extremity of the Sierra Nevada, 

 on the Tehachapi Mountains, and on the east slope of the southern 

 coast mountains, chiefly woodland and brush lands, have been 

 classed as of major watershed-protective influence. The flow of 

 streams from these areas, such as the Mojave and Whitewater Rivers, 

 is rather meager and flashy. The demand for water for irrigation and 

 domestic use exceeds the surface supply. The deficit is made up by 

 pumping water from wells. 



The plant cover, naturally sparse owing to low precipitation and 

 high evaporation, has been so depleted that the basin is exposed 

 to a considerable danger of floods from torrential rains that occur 

 fairly frequently. A storm of more than 7 inches near Tehachapi 

 Pass in late September 1932, caused a flood that killed 15 people and 

 did about $1,000,000 worth of damage to property. Flood discharges 

 from the storm area are reported to have been estimated by engineers 

 of the Los Angeles Flood Control organization to have varied from 

 2,000 to 5,000 second-feet per square mile. Where the rain was most 

 intense, representatives of the California Forest Experiment Station 

 found it washed away 4 to 6 inches of the poorly vegetated surface 

 soil. No gullies were found on areas having a good plant cover. 



SOUTH COAST DRAINAGES 



In the south coast drainage area, which lies west of the summit 

 of the Coast Range and extends from near Santa Barbara to the 

 Mexican border, the water-supply problem is one of the greatest in 

 the United States. Projects planned or actually under way to provide 

 additional supplies for the part of the basin around Los Angeles, as 

 reported in South Coastal Basin, Bulletin No. 32 of the California 

 State Division of Water Resources, will cost in the aggregate close 

 to $350,000,000, exclusive of distribution systems. That report 

 states that in the drainages of the Los Angeles, San Gabriel, and 

 Santa Ana Rivers there are 



* * * 57 incorporated cities, numerous urban communities not incorporated 

 and 2,200 square miles of irrigable land or land suitable for residential develop- 

 ment. About 2,500,000 people, or nearly 50 percent of the population of the 

 State, live in this basin, although the area is less than l%o percent of the total 

 area of the State and only seven tenths of 1 percent of the water supply is found 

 here. Population and irrigated area are rapidly increasing. 



From this it may be inferred that water supply will be the limiting 

 factor in development of the section. It is isolated and remote from other sources 

 and to bring water to it is an engineering undertaking of the first magnitude. To 

 amplify the local supply, the city of Los Angeles has constructed its 250-mile 

 aqueduct to bring in Owens Valley water from the north and. now proposes to 

 extend this to Mono Basin still farther north in order to reach additional supplies. 



