106 SOIL PHYSICS AND MANAGEMENT 



Caldwell Series. The soils range in color from gray to dark 

 gray or black. The subsoils are usually of somewhat lighter shade, 

 varying from light gray to drab, and are underlain by gravel. 

 Small grains, timothy and other grasses, alfalfa, potatoes, and 

 sugar beets are grown. 



Yakima Series. The soils range from light to grayish brown 

 to yellowish brown or light brown in color. They are usually tree- 

 less plains and of alluvial origin. The immediate surface material 

 is derived from, basaltic or other eruptive rocks. 



XI. GREAT BASIN REGION 



This region embraces practically all of the Great Basin of In- 

 terior Drainage. It includes all of Nevada with the exception of 

 the extreme southeastern parts, the western part of Utah, a small 

 part of southwestern Idaho, the south central part of Oregon, and 

 the greater part of the eastern margin of California. 



The region is characterized by numerous isolated ridges and 

 mountain ranges running in a general north and south direction, 

 arid treeless plains and intermittent streams which disappear in the 

 gravelly or sandy soil or discharge into broad lake basins mostly 

 without outlets. Many of these basins were lakes in Quaternary time. 



The soils are classified according to the agencies contributing 

 to their formation. 



(a) Uplands. Bingham Series. This series occupies the 

 lower mountain and upper valley slopes and valley terraces or plains 

 and is formed from mountain wash and delta cone deposits. They 

 are quite fertile when irrigated and are adapted to alfalfa, .grains, 

 sugar beets, vegetables, and fruits. 



(b) River Flood Plains. Jordan Series. The soils are 

 usually dark in color but sometimes light gray or reddish, the 

 heavier lower lying members being underlain by gray, black, yellow 

 or red compact heavy and often calcareous subsoils. They are de- 

 voted to grains, alfalfa, fruits, and truck crops. 



XII. ARID SOUTHWEST REGION 



This region covers the southwestern third of Arizona, a large 

 area in south central New Mexico and in northwestern Texas. It 

 includes also a small area in southeastern Nevada and the south- 

 eastern extremity of California. 



The region consists of sandy, gravelly sloping or flat treeless 

 plains from which rise frequent low rounded hills and occasional 



