Ground-water geology of the Bruneau–Grand View area, Owyhee County, Idaho

The Bruneau-Grand View area is part of an artesian basin in northern Owyhee
County, Idaho. The area described in this report comprises about 600 square
miles, largely of undeveloped public domain, much of which is open, or may be
opened, for desert-entry filing. Many irrigation-entry applications to the Federal
Government are pending, and information about ground-water geology is needed
by local citizens and well drillers, by Federal agencies that have custody of the
land, and by local and State agencies that administer water rights. The areal
geology and ground-water conditions in the Bruneau-Grand View area seemingly
typify several basins in southwestern Idaho, and this study is a step toward
definition and analysis of regional problems in ground-water geology and the
occurrence and availability of ground water for irrigation or other large-scale
uses.

Owyhee County is subdivided physiographically into a plateau area, the Owyhee uplift, and the Snake River valley. The Bruneau-Grand View area is largely
within the Snake River valley. The climate is arid and irrigation is essential
for stable agricultural development. Nearly all usable indigenous surface water
in the area is appropriated, including freshet flow in the Bruneau River, which
is used for power generation at the C. J. Strike Dam. However, with storage
facilities additional land could be irrigated, and some land may be irrigated with
Snake River water if suitable reclamation projects are constructed.

Sedimentary and igneous rocks exposed in the area range in age from Miocene
to Recent. The igneous rocks include silicic and basic intrusive and extrusive
bodies, and the sedimentary rocks are compacted stream and lake sediments.
The rocks contain economically important artesian aquifers; the principal ones
are volcanic rocks in which ground water is imperfectly confined beneath sediments of the Idaho formation, thus forming a leaky artesian system. The altitude
of the piezometric surface of the artesian water does not exceed about 2,700
feet above mean sea level. In some areas, where the land surface is below
that altitude, the artesian system discharges water through springs and seeps
and locally causes waterlogging and development of alkali soil.

In chemical quality much of the water is unsuitable for irrigation and domestic
use. The water contains a relatively moderate amount of dissolved solids, but
the percent sodium and the concentration of fluoride are excessive for some
uses. The quality of the water for irrigation ranges from excellent in the southern part of the artesian system to unsuitable in the northern part. All the
artesian ground water that was sampled contained excessive amounts of fluoride.

There is a substantial supply of undeveloped artesian water in the area, but
sustained use of the water for irrigation may not be feasible unless provisions
can be made for adequate soil drainage and soil amendment, because of the high
percentage of sodium in the water. Detailed hydrologic and geologic study of
the area should precede development.