104 SOIL PHYSICS AND MANAGEMENT 



over the region, but are especially well developed as the wide 

 valleys along the larger streams. The series are as follows : 



Arkansas Series. This series includes grayish brown or dark 

 brown soils, with yellowish brown subsoils resting upon gravels and 

 sands. The substratum is sometimes so near the surface as to 

 cause deficiency of moisture. Soils may be subject to overflow. 

 Wheat, corn, forage crops, and alfalfa are the principal crops. 



Cheyenne Series. The soils are brown with lighter brown or 

 yellow subsoils underlain by sands and gravels. The soils occupy 

 high valley terraces laid down while the streams were choked with 

 ice. They are productive and adapted to grazing, small grains, 

 corn, and potatoes. Under irrigation they grow alfalfa and fruits. 



Laurel Series. The soils are dark gray to brown and the sub- 

 soils are usually lighter in color and are underlain by porous gravel. 

 Corn, small grains, forage, melons and cantaloupes are grown. 



Lincoln Series. The soils are dark brown to dark gray or 

 nearly black, while the subsoils are dark gray to brown. Corn, 

 forage crops, small grains, and alfalfa are grown. More than 

 2,300,000 acres have been mapped. 



Tripp Series. The soils are brown to light gray, while the 

 subsoils are light gray to white. They are of alluvial origin. They 

 are adapted to corn, wheat, oats, potatoes, and vegetables. 



Wade Series. The soils are brown to dark gray, drab or dark 

 brown, while the subsoils are light brown, brown or gray to dark 

 drab, rather heavy and compact. The crops are corn, small grain, 

 flax, potatoes, and alfalfa. 



IX. ROCKY MOUNTAIN AND PLATEAU REGION 



This region covers the areas of elevated mountains and plateaus 

 extending from Canada southward to the lower lying, arid, treeless 

 plains and isolated ranges of the arid region of Arizona and New 

 Mexico. 



The soils vary widely in character owing to the great variety 

 of material from which they are derived and the number of agencies 

 active in their formation. Weathering in places has given rise to ex- 

 tensive areas of residual soils, while at the bases of the mountains 

 large areas of colluvial soils are found. The stream valleys have 

 terraces and flood plains, while the broad intermountain basins 

 have extensive deposits of sediments. 



(a) Uplands. San Luis Series. The soils are reddish 

 brown in color and porous in structure and are underlain by sands 



