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Northern
Gila County
The Northern Gila County Water Plan Alliance formed to develop water
strategies for the area around Payson, Pine and Strawberry along the Mogollon
Rim. The area also is known as the Tonto Creek basin.
The Tonto Creek basin occupies about 920 square miles in central Arizona. The
basin falls entirely within the central highlands province, an area of rugged
mountains composed of igneous, metamorphic, and sedimentary rocks. Formed by
faulting, the basin trends north-south and is drained by Tonto Creek and its
tributaries. The basin is bounded on the north by the Mogollon Rim, on the east
by the Sierra Ancha Mountains, and on the west by the Mazatzal Mountains.
Elevations range from 7,800 feet above mean sea level in the Mazatzal Mountains
to 2,200 feet above mean sea level at Roosevelt Lake where Tonto Creek
terminates.
There are four general rock types in the Tonto Creek basin: alluvium;
basin-fill sands and gravel; Paleozoic sedimentary rocks; and Precambrian
igneous, metamorphic, and sedimentary rocks (Denis, 1981). All four general rock
units in the Tonto Creek basin contain some groundwater reserves. The amount of
groundwater available varies widely, and generally depends on the unit's
composition and structure. The main aquifers are the alluvium and the basin-fill
sediments which contain an estimated three million acre-feet of recoverable
groundwater.
The Precambrian and Paleozoic rock units either contain very little water or
have not been drilled for water; thus, no evaluation of storage can be made.
Little groundwater development has occurred in the basin because 97% of the area
is National Forest land. Most wells are low-yield domestic and stock wells.
According to a 1981 analysis, there are a few irrigation wells, located in the
lower parts of the basin, that pump less than 200 acre-feet per year. Overall,
the U.S. Geological Survey estimated in 1986 that less than 500 acre-feet per
year is pumped from the basin.
Precipitation falling in the higher elevations of the Tonto Creek basin
sustains the base flow of Tonto Creek. The two major aquifers, the alluvium and
the basin-fill sediments, receive most of their recharge by infiltration from
Tonto Creek. Analysts estimated in 1972 that 17,000 acre-feet per year
infiltrate into the aquifers from Tonto Creek. Discharges from the basin include
80,000 acre-feet per year of surface flow, 4,000 acre-feet per year of
subsurface flow discharged into Roosevelt Lake, and 13,000 acre-feet per year of
evapotranspiration from the Tonto Creek floodplain.
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