6 FIELD OPERATIONS OF THE BUREAU OF SOILS, lOl*?. 



gation project of the Office of Indian Affairs. The Casa Grande 

 National Monument and j^art of the Gila Eiver Indian Eeservation 

 also are within the survey. The total extent of the area is 352 square 

 miles, or 225,280 acres. 



The area is made up almost entirely of river bottoms or smooth, 

 nearly level plains, the adjoining mountains having been practically 

 excluded, except for several small hills or buttes. The most promi- 

 nent of these are Twin Butte, Granite Ivnob, part of Cholla Moun- 

 tain, and part of the eastern slope of Pima Butte. The slopes of the 

 included hills are stony and steej). 



Elevations within the area range from about 1,150 to 1,525 feet 

 above sea level. Casa Grande has an elevation of 1,396 feet; Casa 

 Grande Ruins (Casa Grande National Monument), 1,422 feet; 

 Florence, 1,493 feet; and S'acaton, 1,280 feet. 



The Gila River, which crosses the area from east to west, is the sec- 

 ond largest stream in Arizona. The lands lying along this stream 

 are directly drained by it, but the greater part of the area is drained 

 directly by McClellan Wash, which reaches the Gila River within 

 the area. Santa Cruz Wash carries the drainage from the southern 

 part of the area, around Casa Grande, and enters the Gila River a 

 short distance west of the area. The McClellan and Santa Cruz 

 Washes are not everywhere well defined, and they are inadequate to 

 drain a number of large flat areas. The Gila River has a channel 

 varying in width from less than one-fourth mile to a mile or more. 

 The banks of this stream are generally poorly defined and unstable. 

 Shifting of the channels and cutting of the banks take place at each 

 overflow, and the process is increasingly destructive as the stream- 

 bottoms are used more extensively for agriculture. The stream has 

 an average gradient of about 10 feet per mile through the area. 



The McClellan and Santa Cruz Washes are the continuation of the 

 drainage of the Santa Cruz River, which ceases to maintain a definite 

 channel below a point in the southern part of Pinal County, its 

 waters spreading oa er the level plain or flowing slowly down the 

 numerous shallow washes between Picocho Reservoir and Casa 

 Grande. The lands along the McClellan and Santa Cruz Washes 

 are subject to overflow from flood waters that come from the region 

 of Tucson, southeast of the area surveyed. The McClellan Wash 

 has a fall of about 20 feet in its course from the Picocho Reservoir 

 to its confluence with the Gila River. 



The retarded drainage of the southern part of the area gives rise 

 to many shallow lakes or playa flats, which are dry except during 

 heavy rains. These flats are dotted with and bordered by shifting 

 sand dunes. 



In 1910 the population of l^inal County was 9,045 — an increase of 

 16 per cent over that reported in 1900. While the area surveyed 



