Abstract

Numerous wells and a few springs around the perimeter of the Rock Creek Hills (South Hills) south of Artesian City, Idaho, produce water as warm as 49 °C. Warm-water samples throughout the study area share similar chemical characteristics, suggesting a common source of recharge and similar flow systems. Precipitation in the Rock Creek Hills probably infiltrates to depths in excess of 650 m along numerous normal faults and within permeable horizons of the Idavada Volcanics. Underlying Paleozoic rocks are relatively impermeable, except where fractured by recent tectonism, and probably direct the infiltrating ground water toward the lowland of the Snake River Plain. The volcanics have buried a Miocene topographic high that at present separates the warm ground water into two flow systems. Heavy pumping at the edge of the Snake River Plain at present captures the warm-water flow at depth and encourages the infiltration of irrigation water through the Quaternary alluvium and basalt flows of the plain into the underlying Idavada Volcanics.

Several common geotechnical methods proved effective for the reconnaissance exploration of this low-temperature hydrothermal system. Measured temperatures of well and spring water located areas appropriate for study. The measurement of ground-water levels and hydrothermal gradients as defined herein enable the characterization of the warm-water flow systems and the identification of zones of warm-water production. A geochemical survey distinguishes waters with unique chemistries and recharge areas. Reconnaissance geologic mapping and drillers-log interpretation identify the stratigraphic and structural framework controlling the flow systems.

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