SOIL SURVEY OF THE MIDDLE GILA VALLEY AREA, 



ARIZOKA. 



By E. C. ECKMANN, In Charge; MARK BALDWIN and E. J. CARPENTER— 

 Area Inspected by MACY H. LAPHAM. 



DESCRIPTION OF THE AREA. 



The Middle Gila Valley area is situated in the south-central part 

 of Arizona, mainly in Pinal County, only 2 s(|uare miles being in 

 Maricopa County. It lies in a region of isolated or discontinuous, 

 barren, rocky peaks and ranges, mainly of eruptive and crystalline 

 formations, which rise from sloping or nearly level desert plains. 

 This part of the State is recognized physiographically as the Desert 

 region, in contrast to the much higher lying Plateau region of sedi- 

 mentary rocks occupying the northern and northeastern parts of the 

 State. As the title implies, the survey 

 includes the middle valley of the Gila 

 River, which presents a contrast to both 

 the upper valley, in the eastern part of 

 the State, and the lower desert valley above 

 the confluence of the Gila Eiver with the 

 Colorado. 



The area surveyed is irregular in out- 

 line, and roughly Y-shaped. Beginning at 

 the mouth of the Gila River Canyon, about 

 6 miles northeast of Florence, it spreads 

 out westward and southwestward as a fan- 

 shaped area, which is soon divided into 

 two arms by the Sacaton Mountains, 

 which it practically surrounds on the 

 north, east, and south. The northern arm, 

 lying between the Sacaton i\lountains on the south and the Santan 

 Mountains on the northeast, extends westward to Pima Butte. It 

 includes the alhmal bottoms of the Gila River, with parts of the 

 adjacent higher lying plains. The southern arm is confined to a tier 

 of townships extending westward from Picocho Reservoir in town- 

 ships 5 and 6 south to the middle of range 5 east. Small parts of the 

 adjoining townslni)s to the south are also included. The area in- 

 cludes the Sacaton, Casa Blanca, Agency, and Blackwater units, and 

 parts of the Casa Grande and Florence units, of the Gila River irri- 



FiG. 1. — Sketch map showing 

 location of the Middle Gila 

 Valley area, Arizona. 



