SOIL SURVEY OF THE MIDDLE GILA VALLEY, ARIZONA. 



29 



Many of the Indian farmers cultivate parts of the Pima clay, 

 buildinjj their towns and houses on the adjoinin<; terraces of Gila 

 silty clay loam, which are generally affected by alkali. Wheat, bar- 

 ley, alfalfa (PL II, fig. 2), corn, hay, sorghum, truck, and root crops 

 are grown, and good yields are obtained. None of the farmers use 

 fertilizer, and no crop rotation is followed. The type brings as high 

 prices as any in the Gila Yalley. 



In the table below are given the results of mechanical analyses of 

 samples of the soil and subsoil of the Pima clay : 



Mechanical analyses of Pima clay. 



BOUGH STONY LAND. 



Rough stony land consists of steep, rough, and stony areas that 

 have no present agricultural value. It includes various shallow soils 

 occupying buttes and the lower slopes of mountains. The soils are 

 of residual origin, and derived almost entirely from granite, gneiss, 

 mica schist, and associated rocks. There are numerous outcropping 

 ledges, and loose stones and rock fragments of all sizes are abundant, 

 especially around the lower slopes of the buttes and mountains. 



This type is of small extent, as the survey covers only the most 

 desirable agricultural lands of the region. The most important areas 

 lie southeast of Casa Grande, at Twin Butte, and on Cholla Moun- 

 tain. Smaller areas are mapped on small buttes within the area, 

 and on parts of the hill and mountain slopes. 



The vegetation over the greater part of the Rough stony land is 

 sparse and of low grazing value. It consists mainly of cacti of vari- 

 ous kinds, creosote bush, and several other unimportant plants. 



RIVERWASH. 



Riverwash consists of the material occupying the bed of the Gila 

 River. The soil is a mixture of coarse, medium, and fine sands, 

 together with some finer sediments, and differs chiefly from the 

 Riverwash of the Solomonsville area, in the Upper Gila Valley, in 

 carrying less gravel, stones, and coarse sandy material. The type is 

 usually more silty along the edges of the stream bed, where the 

 current is sluggish. 



The boundaries of the strip of Riverwash are very irregular, and 

 in many places they are drawn rather arbitrarily. The surface of 



