A water well (Mineral Materials well) in SE¼ Sec. 33, T28N, R32E has 65.6°C temperatures; 68.3°C water was reported in a drill hole in NE¼ SE¼ SE¼ Sec. 27, T28N, R32E, and hot water was noted in a 10-m-deep shaft about 100 m southwest of this drill hole (Pruss and others, 1961; Everett and Rush, 1965). Mariner and others measured a surface temperature of 61ºC and estimated a reservoir temperature of 128ºC and 169ºC using silica and Na-K-Ca geothermometers, respectively (1982, p. 106). This area is named for the railroad siding of Colado about 10 km northeast of Lovelock. The area is a concealed resource; there are no known surface indications. Geothermal fluids rise to shallow levels in the alluvial area west of the West Humboldt Range. The mountain range here consists of Triassic and Jurassic metasedimentary rocks, primarily phyllite and quartzite, overlain by isolated remnants of Tertiary volcanic and sedimentary rocks (Sibbett and Bullett, 1980; Jones, 1982). No Tertiary rocks have been encountered below the alluvium in drill holes in the Colado area. The northerly trending range is bounded by a complex frontal fault zone; faults are reported to dip 50 to 80° to the west (Sibbett and Bullett, 1980). Thermal fluids appear to rise to shallow levels near drill hole 14-22 (NE¼ SW¼ Sec. 22, T28N, R32E), perhaps along permeable zones resulting from the intersection of northerly and northeasterly striking normal faults that area subparallel to the mountain-front faults to the east. As the fluids enter the alluvium, they flow southwest in shallow alluvial aquifers, down the hydrologic gradient (Sibbett, Christensen, and Bullett, 1983). In 1979 and the early 1980s, 18 shallow gradient holes and two intermediate-depth holes were drilled; a large-diameter well was drilled to 2,427 m in 1981. A bottom-hole temperature of 139°C was reported in that well (Jones, 1982). The highest temperatue reported in a gradient drill hole was 113.5°C at 76 m. Mackelprang (1980, 1982) reported on the interpretation of geophysical data from Colado, and Getty Oil Co. (1976, 1979, 1980) described drill hole data. Christensen (1980) described rock trace-element data from drill holes.