A NATIONAL PLAN FOR AMERICAN FORESTRY 421 



of run-off on floods is more serious on range and sloping agricultural 

 lands than on forest lands. This discussion covers forest land, range 

 and agricultural lands occurring within the forest in such a way that 

 the watershed relationships cannot be effectively separated, and lands 

 cleared of timber that should have remained forested. The following 

 discussion of forest conditions and use will deal both with the timber 

 and its use by cutting and with the forest-range plants and their use 

 by grazing. Destructive factors such as overcutting or improper 

 logging, fire, and overgrazing are considered, as they influence both 

 the timber and the understory of other vegetation. 



SAN JOAQUIN RIVER BASIN 



Water is in especial demand in the San Joaquin River Basin, which 

 includes together with the broad San Joaquin Valley many westward 

 drainages from the southern half of the Sierra Nevada and a narrow 

 strip of the eastern part of the Coast Range. Approximately 

 2,405,380 acres are now irrigated and a total of 3,773,964 acres is 

 irrigable. The Hetch Hetchy project, costing $126,500,000, is de- 

 signed to provide San Francisco and its environs (1930 population, 

 634,394) with an adequate water supply drawn from the Tuolumne 

 drainage of the Sierra Nevada. Many valley towns and cities, also, 

 depend upon the forested watersheds of this basin for their water 

 supplies. Numerous power plants have been developed or are con- 

 templated. On the whole, the water supply is inadequate. 



Toward the southern part of the basin the water shortage is intense. 

 The State water plan proposes to augment supplies in that part from 

 those farther north, through the construction of reservoirs in the 

 Sierra Nevada foothills and of canals to transport the water. 



Approximately 22 percent of the basin's area is occupied by conif- 

 erous forest, which occurs in a belt along the west slope of the Sierra 

 Nevada. It is from this belt that most of the water comes. The 40 

 to 50 inches or more of precipitation in the northern part and the 20 

 to 30 inches in the southern part occur chiefly as snow, which accumu- 

 lates, particularly in the northern part, in such a way as to furnish 

 large reserves for summer flow. In the main, timber stands are dense 

 and there is a good litter cover which, together with undergrowth, 

 completely covers the soil. Accordingly, snow melt is retarded and 

 there is good absorption into the soil. Normal erosion of the soil, 

 which is derived largely from granitic rocks, does not exceed soil 

 formation unless the cover of vegetation is removed. All this area 

 has been classed as of major watershed influence. In the heavily 

 forested belt, which is chiefly included in national forests or national 

 parks, watershed conditions are generally good. National-park 

 management aims to keep the forest in as natural a condition as 

 possible, and national-forest lands are administered to maintain water- 

 sheds in the most satisfactory condition feasible. 



In the foothills where the woodland and brush types occur, an 

 exploratory survey by the Forest Service indicated that abnormal 

 erosion is very serious even though rainfall totals only 15 to 25 inches. 

 Much of the woodland and brush area has passed into private owner- 

 ship, although parts of it remain as unappropriated public domain. 

 Fire is the greatest threat to the woodland cover. A great part of the 

 foothill belt is burned yearly. Many fires are set by stockmen in 



