In the late 1970s and early 1980s, Phillips Petroleum Co. drilled about 36 shallow temperature-gradient drill holes and two deeper slim holes in an area north and west of North Valley. These drill holes identified a subsurface geothermal anomaly over about 75 km2 that is centered on an area about 3 km southwest of Black Warrior Peak. One 300 m drill hole had a temperature of 51ºC, and a maximum temperature of 129.4ºC was reported at a depth of 552 m (GeothermEx, 2004). Location: 39.90ºN, 119.22ºW.