Temperature gradient drill holes drilled by Phillips Petroleum in the 1980s outline an area of thermal groundwater at the north end of Granite Springs Valley (Richards and Blackwell, 2002; GeothermEx, 2004). An isothermal temperature of 89.7°C was logged in one well between ~1,700 ft and 1,805 ft depth (maximum drilled). Location: 40.22ºN, 118.92ºW.