42 CONSERVATION OF GROUND WATER 



over the low drainage basin. Ground water is everywhere 

 more than 75 feet below the surface, and there is no evi- 

 dence of ground-water discharge from the basin. 



One of the most important industries in the Sonoran 

 Desert area is the mining and milling of the low-grade 

 copper ores at Ajo, Ariz. The Phelps-Dodge properties there 

 in 1940 required about 240 gallons of water per ton of ore 

 mined, of which about three-quarters was used in concen- 

 trating the ore. To meet these requirements, the company 

 pumps several million gallons a day from a "water mine," 

 consisting of two shafts and several thousand feet of drifts 

 in permeable lava more than 600 feet below the land 

 surface. 



Although there may be some replenishment from tor- 

 rential rainstorms over the higher parts of the drainage 

 basin, the quantity recharged is far less than the with- 

 drawals; since large-scale operations commenced in 1917, a 

 considerable volume of the aquifer has been unwatered by 

 extension of drifts and by pumping from deeper levels. 

 Thus, there has been a depletion of water reserves by min- 

 ing more or less comparable to the depletion of copper re- 

 serves. 



Farther north in Arizona, pumpage of water for irriga- 

 tion is increasing in Bouse Valley and Centennial Valley, 

 where preliminary reconnaissance indicates that replenish- 

 ment to the ground-water reservoirs may be so low as to be 

 considered negligible. 



The valley ground-water reservoirs of the West are typically 

 bordered on two sides and sometimes completely enclosed by 

 mountain ranges, from which both the water and the water- 

 bearing material are generally derived. In many instances one 

 range is far higher than the other and furnishes the great bulk 

 of the water to the valley. As a result, the water from one side 

 may saturate the valley materials clear to the base of the un- 

 productive range on the other side, as is the case in Utah Val- 

 ley in Utah. Commonly, however, the sediments in the central 



