Melinda K. Cuff | Geology Reports

USGS1987

Ground-water conditions in Avra Valley, Pima and Pinal Counties, Arizona -1985

Avra Valley is a north-trending alluvial basin about 15 mi west of Tucson in Pima and Pinal Counties in south-central Arizona. The valley includes about 520 sq mi of which about 100 sq mi is in the San Xavier Indian Reservation. The basin is bounded on the east by the Tortolita, Tucson, and Sierrita Mountains and on the west by the Picacho, Silverbell, and Roskruge Mountains. The climate of the valley is semiarid, the average annual precipitation ranges from 8 to 12 in., and the average annual lake evaporation ranges from 58 to 62 in. Two major ephemeral streams--Santa Cruz River and Brawley Wash--drain the area. Santa Cruz River and Brawley Wash and their tributaries provide a source of recharge to an extensive alluvial aquifer that underlies the valley floor. Since 1940, the amount of groundwater pumped from the aquifer has been greater than the amount of natural recharge from infiltration and underflow. Overdraft of the aquifer resulted in substantial water level declines throughout the valley. Until 1969, use of groundwater in Avra Valley was for irrigation. Since 1969, the city of Tucson has pumped and transported groundwater for municipal use in the adjacent Tucson basin from lands that were purchased and retired from agriculture. The purpose of this report is to describe groundwater conditions in Avra Valley as of 1985. A brief discussion of the geohydrologic setting and history of groundwater development are given to define aquifer characteristics, changes in groundwater levels, and groundwater pumpage since 1940. (Lantz-PTT)

Arizona↗

USGS1984

Geohydrologic conditions in the Vekol Valley, Pinal and Maricopa Counties, Arizona-1983

Vekol Valley is a north-trending valley in south-central Arizona. The valley includes 270 mi 2 and is bounded by the Table Top and Vekol Mountains on the east, the Sand Tank and Maricopa Mountains and the White Hills on the west, and the Both and Haley Hills on the north. The climate is semiarid and precipitation occurs as local summer thunderstorms and regional winter storms. The average annual precipitation is 7 to 8 in., and the potential evaporation rate is about 10 times that of the average annual rainfall (Sells and Hill, 1974, p. 7, 44). Storm runoff occurs mainly as sheetflow and floods of short duration. Although some runoff is diverted into catchment tanks for use by livestock, runoff is not used for irrigation or public supply. Vekol Valley is underlain by a thick sequence of basin sediments, sedimentary rocks, and volcanic rocks. The surrounding mountains are composed of crystalline and volcanic rocks, which also underlie the basin sediments to form the sides and bottom of the basin. The valley is divided into a northern part and a southern part by a bedrock outcrop of crystalline rocks between the White Hills on the west and the Table Top Mountains on the east (R. P. Wilson, 1979, p. 8). The northern part is about 90 mi 2 (J. R. Marie and K. J. Hollett, U.S. Geological Survey, written commun., 1984) and the southern part is about 180 mi 2 . The hydrologic data on which this map is based are available, for the most part, in computer-printout form and may be consulted at the Arizona Department of Water Resources, 99 East Virginia, Phoenix, and the U.S. Geological Survey offices in: Federal Building, 301 West Congress Street, Tucson , and 3788 North 16th Street, Suite E, Phoenix. Material from which copies can be made at private expense is available at the Tuscon and Phoenix offices of the U.S. Geological Survey.

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