Telephone Well is located in Copper Valley, which makes up the southern end of Granite Springs Valley north of the Trinity Range. Phillips Petroleum Co. drilled about 36 temperature-gradient wells and two slim holes over an area of 50 km2 in the vicinity of Telephone Well in the 1980s (SMU; Sass and others, 1999; Richards and Blackwell, 2002). The wells have temperatures up to 45.6ºC at about 190 m (GeothermEx, 2004). Location: 40.00ºN, 119.03ºW.