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.