Temperature-gradient drill holes drilled by Phillips Petroleum Co. (10 holes scattered across 9 Sections in the vicinity of Fireball Ridge) have anomalous gradients and temperatures up to 30ºC at depths of 91 m (SMU; Sass and others, 1999; GeothermEx, 2004). Gradients of about 100-150ºC/km were reported from drill holes at the north end of Fireball Ridge (GeothermEx, 2004). Location: 39.92ºN, 119.07ºW.