Structure of Railroad Valley, Nye County, Nevada

William J. Ehni

In 1976, the second oil field in Nevada--Trap Springs--was discovered in Railroad Valley. Since then, more than 100 oil wells have been drilled in Nye County, and most of these have been in Railroad Valley. This well-control helped to unravel the complex structure of Railroad Valley and enabled the construction of more accurate maps of this valley than any other. This information can be used to construct models for exploring other valleys in the Basin and Range Province of eastern Nevada.

The basic stratigraphy of the valley consists of Paleozoic carbonates and shales overlain by Tertiary volcanics, overlain, in turn, by valley fill. The areal extent of Tertiary volcanics, which can be a good reservoir rock, is controlled by tensional normal faulting and paleotopography. In some areas, these volcanics can be in excess of 5,000 ft thick, but absent within a few miles, owing to paleotopography and/or faulting. The Paleozoic rocks are deformed by a pre-basin and range compressional history that folded and faulted them. As a result, the structure within the Paleozoics is more complex. Thrust faulting played an important role in the deformation of these rocks. Crystalline basement rocks can be found juxtaposed between Paleozoic outcrops in the flanks of the valley, and Pale zoic rocks found in well control farther out in the valley.

The geothermal history of Railroad Valley plays in important role in constructing a structural map of the valley, taking into account the Mesozoic thrust faulting and Tertiary normal faulting. Air photos, combined with good well control and published reports, assist in mapping the geologic structure in Railroad Valley.

AAPG Search and Discovery Article #91040©1987 AAPG Rocky Mountain Section Meeting, Boise, Idaho, September 13-16, 1987.