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Upper Hassayampa Basin
The Upper Hassayampa basin includes about 740 square
miles of the Central highlands physiographic province of central Arizona and
contains relatively small basins filled with alluvial deposits. The basin is bounded on the north by the Weaver Mountains, on the
northwest by the Date Creek Mountains, on the south by the Vulture Mountains,
and on the east by the Bradshaw Mountains. The mountains are composed of crystalline and sedimentary rocks. Elevations in the area range from 2,000 feet to over 7,000 feet above
mean sea level.
The main water-bearing unit is the basin-fill deposits
which is found in the valleys between the mountains. These deposits consist of gravel, sand, silt, and clay and
may yield several hundred gallons per minute to wells. Where fractured, the crystalline and consolidated sedimentary
rocks which make up the mountains may yield less than 10 gallons per minute
(Sanger and Appel, 1980). In the
alluvial basin north of the Vulture Mountains, the main water-bearing unit
ranges from a few tens of feet thick near the margins to over 1,000 feet thick
toward the middle (Sanger and Appel, 1980). In a few areas along the Hassayampa River, the crystalline rock is
overlain only by a thin cover of stream deposits. Near Wagoner, these deposits are up to 135 feet thick (Sanger
and Appel, 1980).
Depth to groundwater varies across the basin. Water levels range from a few feet below land surface along the
Hassayampa River to over 1,000 feet below land surface toward the middle of the
basin. Approximately 1.1 million
acre-feet of groundwater are in storage (to 1,200 feet below land surface). An estimated 1,450 acre-feet of groundwater were pumped from the basin in
1985 (Arizona Department of Water Resources, 1988). Most of the pumpage was for irrigation, domestic, stock and public supply
purposes. Despite groundwater
pumpage there has been little regional decline in water levels in the basin
which suggests the area is still in a steady state condition. Large short-term changes in water level do occur, however, where water
levels are directly influenced by precipitation and streamflow. Water quality is generally good. In
most wells dissolved solids concentrations are below the maximum contaminant
level set at 500 milligrams per liter for public supplies. Fluoride concentrations, however, exceed the maximum contaminant level in
some areas (Sanger and Appel, 1980).
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