Traditionally, geothermal power plants have been located in areas along tectonic plates where hot springs and other indications of thermal activity can be seen at the surface (Figure 1). However, EGS can be used in areas where hot rock can be found at reasonable depths; well depths of between 4–6 km would allow EGS in many parts of the U.S. Wells are drilled into the hot subsurface rock; fluid is then injected, heated by contact with the hot rock, and removed to power turbines at the surface.