Vekol Valley is a north-trending valley in south-central Arizona. The valley includes 270 mi² 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 mi² (J. R. Marie and K. J. Hollett, U.S. Geological Survey, written commun., 1984) and the southern part is about 180 mi².

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.