Cenozoic Geology And Geothermal Systems Of Southwestern Utah

This 27-page report analyzes new detailed (1:12,000 scale) geologic mapping of a 14 square mile area centered by the high-temperature (350°F) Sulphurdale heat source, which at the surface makes up a circular area about a mile in diameter that is likely caused by a magma body at depth. A former small steam-driven geothermal electric power plant in the circular area is being replaced by a larger plant (Enel Green Power North America) that will use binary technology. Five cross sections tied to and at the same scale as the map help interpret the likely extent of the geothermal resource. Sulfur derived from evaporites at depth was initially mined at a solfatara above the heat source; associated sulfuric acid seeped downward to remove the Kaibab Limestone and Toroweap Formation from the subsurface.

This report describes the geology of the central Virgin River basin in southwestern Utah, and characterizes the structure and lithology of the Jurassic Navajo Sandstone and the thickness and stratigraphy of Quaternary-late Tertiary unconsolidated deposits, the two main aquifers in the region. Southwestern Utah has experienced rapid population growth and increased demand on water supplies during the past 15 years, and the purpose of this report is to better define the ground-water resources of the area. Ground water provides approximately half of the public water supply in southwestern Utah, so future decisions regarding water use must be based on careful geologic characterization of the aquifers and their relation to the regional hydrologic system. The results of this study will be applied to ground-water modeling, evaluating regional and local hydrogeologic conditions, and assessing sites for development of ground water. 53 pages + 7 plates

This 23 page report is an initial investigation into the role that low-angle faulting may play in the formation of the Thermo Hot Springs Known Geothermal Area (KGRA), within the Sevier geothermal anomaly of southwestern Utah. The stratigraphy and structures exposed in the southern mineral mountains are used as an analog for studying the subsurface stratigraphy and the detachment fault within the Thermo Hot Springs KGRA.