In 1978 the withdrawal of ground water was about 4.2 million acre-feet in Arizona, and slightly more than 3.4 million acre-feet of ground water was used for the irrigation of crops. The amount of ground water withdrawn in 1978 decreased more than 1.2 million acre-feet from the amount withdrawn in 1977 and is the smallest amount withdrawn since the mid-1950 's except in 1966. Nearly all the decrease was in the amount of ground water used for irrigation in the Basin and Range lowlands province. Possible causes for the decrease include above-average precipitation, greater availability of surface water, and some comparatively new conservation practices. The Salt River Valley and the lower Santa Cruz area are the largest agricultural areas in the State; the amount of ground water withdrawn for agricultural use in the Salt River Valley and the lower Santa Cruz area decreased nearly 613,000 and 291,000 acre-feet, respectively, between 1977 and 1978. The report contains two small-scale maps of Arizona that show (1) pumpage of ground water by areas and (2) the status of the ground-water inventory in the State. The main map, which is at a scale of 1:500,000, shows potential well production, depth to water in selected wells in spring 1979, and change in water level in selected wells from 1974 to 1979. The brief text that accompanies the maps summarizes the current ground-water conditions in the State. (USGS)
