SOIL SURVEY OF CHE MIDDLE GILA VALLEY, ARIZONA. o7 



tj^pes liHve more friable subsoils, contain more organic matter, and 

 are more poorly drained than those of the old valley-filling group. 

 The Gila soils are brown and underlain by a permeable subsoil; the 

 soils of the Pima series have similar characteristics except color, 

 Avhich is darker. Alkali is present in places in both these series. The 

 soils are overflowed and have a high water table. 



Irrigation is necessary to insure crops in this region. In 1910 

 there were 25,431 acres under irrigation. Practically all the water 

 for irrigation is obtained by gravity from the Gila Kiver. This is 

 generally of good quality. Water is also obtained from wells. This 

 may be somewhat higher in soluble salts than the river water. Stor- 

 age of the waters of the Gila River is necessary to the permanent 

 development of the desert lands. 



More than 50 per cent of the lands in this area contain more or 

 less alkali. Sodium chloride, sodium sulphate, and sodium carbonate 

 predominate in the alkali crust. Sodium chloride is by far the most 

 abundant. The chief alkali areas occur at the lower levels, in the 

 western and southwestern parts of the survey. The largest alkali - 

 free areas occur northeast and east and to the west of McClellan 

 Wash, Alkali-free areas also occur along the Southern Pacific Rail- 

 road and on the mountain and foothill slopes. 



o 



