Abstract

Snake Valley is a 95-mile-long (150 km) valley in Utah and Nevada that holds great interest for residents of both states because of its ground-water resources. The geologic framework of Snake Valley and adjacent Hamlin Valley, Tule Valley, Pine Valley, Fish Springs Flat, and Wah Wah Valley and their surrounding ranges was analyzed as part of an effort to characterize ground-water conditions and regional ground-water flow. The study area lies within the boundary of the Great Salt Lake Desert regional ground-water flow system, in which the valleys are hydraulically interconnected and ground-water movement is northward to the Great Salt Lake Desert. Snake Valley is bounded on the west by high ranges: the Deep Creek Range of Utah and the Kern Mountains and Snake Range of Nevada. The ranges consist mostly of Proterozoic and Cambrian quartzite intruded by Jurassic, Cretaceous, and Tertiary plutonic rocks. Uplift occurred during late Cenozoic time along mostly high-angle basin-range normal faults, at which time the upper part of the Snake Range failed along the Snake Range decollement, a low-angle normal denudation fault. The east side of Snake Valley is bounded by the low Confusion Range and adjacent ranges of mostly middle to upper Paleozoic carbonate rocks that were folded and locally thrusted during the late Mesozoic to earliest Tertiary Sevier compressive deformational event. Hamlin Valley, south of and tributary to Snake Valley, is bounded on the northwest by the low Limestone Hills, made up of faulted Devonian carbonates, through which some ground water may flow from Spring Valley to Hamlin Valley. Southern Hamlin Valley drains the large Oligocene Indian Peak caldera complex. East of Snake Valley is Tule Valley, on the east side of which are the narrow, sharp Fish Springs and House Ranges, which consist mostly of Cambrian quartzite and carbonate rocks. Pine Valley to the south is bounded on its east side by the Wah Wah Mountains, made up of locally thrusted, east-dipping Cambrian quartzite and carbonates overlain by Oligocene ash-flow tuffs. Fish Springs Flat lies east of Tule Valley, between the Fish Springs Range on the west and the Dugway and Thomas Ranges on the east. The Dugway and Thomas Ranges consist of Eocene ash-flow tuffs and Miocene rhyolite flows that overlie Paleozoic carbonates. Wah Wah Valley to the south is bounded on the east by Proterozoic quartzite, an Oligocene stock, and Oligocene tuffs and flows in the San Francisco Mountains and low hills farther south. As in most places elsewhere in the Great Basin, the six valleys are north-trending grabens, and the ranges are north-trending horsts, formed during the late Cenozoic basin-range extensional deformational event. This deformation, resulting in the present topography, was formed by large northerly trending, high-angle, basin-range faults. Snake Valley was downfaulted thousands of feet relative to adjacent ranges, followed by erosion of the ranges and deposition of basin-fill sediments in the valley. In most places in the interior of Snake Valley, the sediments are as much as 5000 feet (1500 m) thick, but the sediments are thicker in some subbasins. The other five valleys have comparable to lesser thicknesses of sediments. We apply the concept of fracture flow, developed from extensive mapping experience in the Basin and Range Province, to explain ground-water movement. Under this concept, ground-water flow is enhanced by the north-trending faults and parallel fault-related fractures in basin-fill deposits and underlying bedrock units. The faults act as conduits to northerly flow and as partial barriers to east or west flow. Aquitards in many of the ranges include the Proterozoic and Cambrian quartzite, plutonic rocks of several ages, and the Chainman Shale and Thaynes Formation, which further restrict or prevent east or west ground-water flow.