78 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



lava and in some cases granitic rocks. Some are derived from 

 ancient lake beds. 



12. Rocky Mountain Valleys, Plateaus and Plains. These 

 soils are derived from a great variety of igneous, metamorphic, 

 and sedimentary rocks. The soils of the mountain slopes are 

 usually of little agricultural value, while those of the plateaus, 

 valleys, and plains range from grazing land of low value to soils 

 adapted to fruit, sugar beets, and other special crops. 



13. Pacific Coast. Soils found in this region range from 

 residual and colluvial soils of the mountain sides, foot slopes and 

 foot hills, to deep and extensive river flcod plains and delta sedi- 

 ments, and ancient and modern shore and lake deposits. Their 

 value depends largely upon possibilities of irrigation, and local 

 conditions of rainfall and temperature. 



