424 A NATIONAL PLAN FOE AMERICAN FORESTRY 



exposed. Very severe sheet and gully erosion is occurring, for ex- 

 ample, on slopes cleared for cultivation. Most of the higher Coast 

 Range forest areas have been considered as having a major watershed- 

 protective influence. Areas classed as of moderate influence are 

 those draining more directly into the Pacific Ocean. 



CENTRAL COAST DRAINAGES 



Coniferous forest occupies less than 8 percent of the central coast 

 drainage area, which extends along the Coast Range from San 

 Francisco Bay to about 20 miles southeast of Santa Barbara. The 

 coniferous forest is largely confined to areas near the coast where 

 precipitation is rather heavy, averaging 25 to 40 inches annually. 

 The woodland and brush types occupy approximately 40 percent of 

 the drainage area, in general the portions where precipitation averages 

 from 15 to 25 inches annually. They cover the bulk of the steep 

 Coast Range slopes. 



Demand for water for municipal and domestic use is heavy. It is 

 from the northern part of this basin, the Spring Valley development, 

 that San Francisco obtains a large part of its water supply. Many 

 communities depend upon wells, the water table of which is dropping, 

 and will require new storage. In the southern part of the basin there 

 is a shortage of water to meet the demand for domestic, industrial, 

 and irrigation supplies. 



Fires in the chaparral, brush, and forest cover in these drainages 

 are sometimes disastrous. A record fire that occurred during the fall 

 of 1932, resulting from carelessness of a recreationist, consumed the 

 forest cover on more than 200,000 acres in the southern part. The in- 

 evitable, silting from erosion of fire-devastated slopes will seriously 

 threaten the permanency of the Santa Barbara and Montecito reser- 

 voirs. The seriousness of this prospect is suggested by the silting of 

 the Gibralter Reservoir of the city of Santa Barbara that has followed 

 fires. 



In 1923 and 1925 fires destroyed the brush and small-tree cover on 

 40,000 acres, or 30 percent, of the 133,000-acre drainage basin of this 

 reservoir. By 1928, sediment washed into the reservoir by erosion 

 from the burned area amounted to 6 percent of the reservoir's storage 

 capacity, and large quantities of sand, gravel, and boulders were piled 

 along the streams in position to be washed down in future years. 

 In 1932, silt deposits occupied more than 14 percent of the reservoir's 

 original capacity. Since construction of the reservoir cost $57.50 per 

 acre-foot of storage space, these erosion deposits have cost the city 

 $120,750 in the 10 years since completion of the project. The loss of 

 investment in storage in the Gibralter Reservoir, in 10 years, has been 

 more than $3 for every acre burned. Silting from a drainage densely 

 covered by brush is comparatively slight. The entire forested area 

 in this basin has been classed as having a major watershed-protection 

 influence. 



DESERT BASIN 



Of outstanding importance in the desert basin, which includes much 

 of the southeastern part of California, is the maintenance of as ef- 

 fective a cover as possible on the Owens Valley watershed, from which 

 the city of Los Angeles obtains water. The east slope of the Sierra 



