Hot springs are found in Quaternary alluvium in SW¼ SW¼ SW¼ Sec. 15, T24N, R47E (projected, Simpson Park Mts 30ºx60º sheet) along the west side of Grass Valley (Lander County). Chemical analyses conducted by Ormat in 2005 on 90.5°C hot spring discharge indicate a 177°C reservoir based on silica geothermometery. As part of the DOE GRED (Geothermal Resource Exploration & Definition) program, Ormat refined a geologic model with the use of mapping, gravity, magnetics, drilling of shallow gradient holes and stress field analysis. About 760 m northeast of the springs a concealed, northeast-trending speculative fault is defined by anomalous soil gas mercury and geophysical methods. Hot water is thought to migrate up the fault and flow southeast down the hydrostatic gradient to the hot springs (Matlick and Morris, 2005).