422 A NATIONAL PLAN FOR AMERICAN FORESTRY 



the belief that fire will keep the brush cover open and improve grazing 

 or by owners for the purpose of clearing land. The effect of destroying 

 cover by fire has been excessive loss of soil from heavy rains. As was 

 stated earlier in this section, this loss amounted to 4 cubic yards of 

 soil per acre on experimental plots near Northfork during one winter 

 rainy period, during which only the barest trace of detrital material 

 was washed from adjacent unburned woodland plots. 



Woodland areas in the foothills furnish winter grazing for herds 

 that occupy higher range during the summer months. Long, dry 

 summers normally make it difficult for forage to grow, and the recent 

 series of dry years has so depleted the forage cover on these vital 

 watersheds that the problem of range feed supply and erosion control 

 has become alarming. Studies recently begun in the foothills by the 

 Forest Service are indicating why overgrazing has often been destruc- 

 tive to forage and watershed values there. Annual plants begin 

 growth immediately following the start of winter rains, and livestock 

 are usually placed on the range at that time. Growth in early winter 

 is extremely slow ; and the scant vegetation, depleted by overgrazing, 

 does not effectively protect the soil against erosion from heavy rains. 

 In addition, accelerated erosion has resulted from the clearing for 

 agricultural development of certain sloping lands that should have 

 remained in woodland. Because of the great danger of erosion when 

 the vegetation is depleted, and the seriousness of the erosion damage 

 to irrigation enterprises as well as of loss of soil productivity on the 

 eroded lands, woodland and brush areas in the foothills have been 

 classified as of major watershed-protective influence. 



SACRAMENTO RIVER BASIN 



The broad, rich, irrigated Sacramento Valley is bordered by moun- 

 tains rising in a semicircular belt. Precipitation in the mountains 

 is heavy, in general, occurring largely in winter as snow which at the 

 higher elevations accumulates to considerable depths. Over most 

 of the westward slopes of the Sierra Nevada, annual precipitation 

 varies from 40 to 75 inches. On the plateau area in the northeastern 

 part of the State drained by the Pitt River it varies from 15 to 35 

 inches. Along the east slope of the Coast Range it varies from about 

 20 to 35 inches. The melting of heavy snows furnishes abundant 

 run-off for irrigation and power, especially in the spring and early 

 summer. Rapid melting of the snow pack or heavy rains may cause 

 damaging floods; for example, as has previously been mentioned, the 

 March 1928 floods in the Sacramento Valley caused a loss of $736,000. 



About 40 percent of the Sacramento River Basin is occupied by a 

 dense forest of conifers. This coniferous forest develops a thick 

 ground litter of needles and twigs. A rather dense stand of under- 

 growth, largely brush, also occurs. Where the vegetative cover has 

 not been devastated by fire, destructive logging, or excessive grazing, 

 it is effective in regulating run-off, and especially in preventing 

 erosion, and is classed as of major watershed influence. On areas 

 covered with partly decomposed lava and largely level, especially on 

 the plateau in the northeastern part of the State, moisture readily 

 penetrates the soil and the danger of serious erosion is slight. On 

 such areas the forest, which is largely ponderosa pine, is considered 

 to influence watershed values but slightly. Much of the Coast 



