NATIVE FORAGE GRASSES 143 



strongly alkaline there is always some vegetation even 

 though the rainfall is very low. Areas of drifting sand 

 and of rock are devoid of vegetation, one because of the 

 instability of the soil, the other because of its absence, 

 and not because of the absence of water. In the regions 

 thus far mentioned under deserts there is no grazing. 



In a general way the remaining desert areas furnish 

 some grazing at certain periods of the year. Much 

 desert land is excluded from actual use because there is 

 no water supply for stock. Portions of such regions are 

 gradually being brought into usefulness by the boring 

 of wells and the discovery of artesian water supply. 



Throughout the region from the Sierra Nevada Moun- 

 tains to the Rocky Mountains, the plateau is a desert 

 region at the lower altitudes (excluding the vicinity of 

 the streams) with humid forests upon the numerous inter- 

 spersed mountain ranges. The snow fall, except in the 

 southern part of the region, affords a supply of water 

 for stock during the winter, hence it is customary to 

 range sheep upon the desert in winter and upon the 

 mountains in summer. The forage upon the desert in 

 winter is chiefly shrubs and coarse perennials that are 

 not grasses. 



In southern California, Arizona, and New Mexico 

 annual plants, including several small annual grasses, 

 are important sources of forage following the short rainy 

 season. In the eastern part of this region the rain comes 

 mostly in the summer, hence there is a short period of 

 summer grazing. In the western part the rains come in 

 the winter, with a corresponding winter grazing season. 

 There is an intermediate region where the seasons over- 



