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Fly Ranch (Ward's, Hualapai Flat Hot Springs)(updated 2004)

Ward's or Fly Ranch Hot Springs are located in Hualapai Flat about 24 km north of Gerlach (mainly in Secs. 1, 2, T34N, R23E). The springs are the largest in northwestern Nevada, discharging into 30 to 40 pools over an area of 30 hectares. The surface flow is used for irrigation (Sinclair, 1962b). A number of warm-water wells are also present in the area (Harrill, 1969).

The oldest rocks in the Hualapai Flat area are Permian and Triassic metavolcanic and metasedimentary rocks ( figure) that have been tentatively correlated by Bonham (1969) with the Happy Creek volcanic series in Humboldt County. Cretaceous granodiorite intrudes the sequence to the south in the Granite Range. In the vicinity of Hualapai Flat, the Tertiary is represented by a sedimentary unit of tuffaceous sands and air-fall tuffs; this is overlain by a finely crystalline, black basalt. Elsewhere in the vicinity andesitic to rhyolitic flows and tuffs also underlie the basalt. Grose and Keller (1975b) also described a number of different Quaternary units.

North- and north-northeast-trending normal faults cut all of the lithologic units, and late Quaternary fault scarps and tectonic cracks transect the floor of Hualapai Flat, which is a small structural-topographic basin (Sperandio and Grose, 1976). Many of the normal faults occur along the western side of Hualapai Flat and have their eastern sides downthrown. Displacements appear to be dip slip, amounting to meters to 10s of meters on any one fault, but totaling thousands of meters between the Tertiary volcanic rocks and Cretaceous granodiorite along the southwest margin of Hualapai Flat (Grose and Keller, 1975).

The faults at Hualapai Flat are believed to be part of a regional and probably deep-seated fault zone that may extend 64-72 km from Winnemucca Lake north along the west side of the Selenite Range, through Gerlach Hot Springs, along the east side of the Granite Range, along the west side of Hualapai Flat, and northward to High Rock Lake. Sperandio and Grose (1976) suggested that the localization of the thermal anomaly at Ward's Hot Springs is probably due to deep hydrocirculation along deep-seated fractures where the north-south fault zone intersects a major northwest-trending fracture system that terminates the north end of the Granite Range west of Hualapai Flat. Quaternary alluvial units in Hualapai Flat record rifting, normal faulting, and subsidence in Late Quaternary (Grose and Keller, 1975a). These features indicate extension of the area, generally along a northwest-southeast axis. The development of the thermal system at Ward's Hot Springs is favored by this extensional tectonic regime, and the major spring area is located on the upthrown side of a 4.4-km-long fault scarp that has a maximum relief of 10 m.

Spring deposits at Ward's Hot Springs reportedly consist of both siliceous sinter and calcareous travertine (Sinclair, 1962b). A shallow well (the "Geyser Well") was drilled in the hot spring area in 1916 and has been discharging steam and boiling water since that time. The water is highly mineralized and precipitation of the chemical constituents at the surface has created a tower of travertine 5 m high. Nearby Fly Ranch Geyser is not a natural phenomena either, but results from the leaking of a geothermal well drilled by Western Geothermal in 1964. The red and green colors of the travertine represent two different species of thermophillic algae (Flynn and others, 1979). Water temperatures in wells and springs of the hot springs area and vicinity range from near normal to over 104.4°C, and Mariner and others (1974) reported a 125°C estimated minimum thermal reservoir temperature using the silica geothermometer. In 1964, Western Geothermal, Inc. drilled a 300m deep well (Fly Ranch No. 1(?)) nearby, and in 1979 a 1,589-m large-diameter geothermal well (the Sunoco Energy Development Co. Holland Livestock Ranch No. 1-2-FR in NE¼ NE¼ Sec. 2, T34N, R23E) was drilled near the spring area. The Holland Ranch well reached temperatures of about 94ºC at 365 m; this temperature was maintained to total depth (GeothermEx, 2004, Fig. FLY00-2).

Map 1

Map 2