A number of hot springs are located in alluvium along the west side of the Black Rock Range (figure). These springs are normally 1.6 km or less from the bedrock outcrops and are aligned along an 11-km-long zone from south of Black Rock Point to Double Hot Springs (Hose and Taylor, 1974). The springs are along a major range-boundary fault with slight Holocene displacement that extends north from Black Rock Point to Soldier Meadows, a distance of about 56 km. A hot spring is also present in Sec. 10, T37N, R26E about 8 km north of Double Hot Springs (Waring, 1965), and warm ground was encountered about a kilometer north of that spring in a U.S. Geological Survey test hole (Olmsted and others, 1975). Thus, the known extent of the thermal anomaly is about 19 km. No data are available for the northern portion of the boundary fault. To the south of Black Rock Point the fault crosses the Black Rock Desert (figure) and joins with a fault associated with the hot springs at the Trego area in Pershing County (L. T. Grose, written commun., 1977). Hose and Taylor (1974) suggested that the Holocene displacement on this fault may be related to an earthquake of magnitude 4.1 at 41°N, 119°W in 1936. The hot springs along this zone were used for drinking, bathing, and stock watering by wagon-train emigrants (Paden, 1949) on the Applegate-Lassen Trail. Today they are used for stock watering and irrigation.
Water wells on the west side of the Black Rock Desert, 6-12 km northeast of Double Hot Springs, are also reported to be warm. The wells are in Secs. 10, 11, and 26, T37N, R25E (Sinclair, 1963a; Grose and Keller, 1975b), and range from 36.1ºC and 39.4ºC for the northerly wells to 25.6ºC and 22.2ºC for the southerly ones. Wagner Spring (SE¼ NW¼ Sec. 4, T37N, R25E), located about 2.5 km north of the Sec. 11 wells, is also reported to be warm (Williams, 1996, p. 16).
The nearest young volcanic rocks are the less than 6-million-year-old basalts 64-80 km to the north along a north-northeast-trending lineament that runs from Soldier Meadows to Railroad Point (figure). The Double Hot Springs-Black Rock Hot Springs fault appears to turn to the northeast and join this lineament just west of Soldier Meadows Hot Springs.
Higher concentrations of dissolved solids are reported in springs near the south end of the fault. This is believed to be due to contamination of the waters by more saline brines that probably collect in low areas of the Black Rock Desert (Hose and Taylor, 1974).
Estimates of the subsurface aquifer temperature based on SiO2 content show reasonably consistent temperatures for springs at either end of the fault. These estimated aquifer temperatures at the Double Hot Spring is 140°C (Hose and Taylor, 1974). Trace amounts of both travertine and siliceous sinter are reported (Hose and Taylor, 1974).
Water temperatures at springs along the fault are usually 54.4 to 76.7°C, with temperatures up to 94.4°C, which is boiling for this elevation (1,220 m), reported at the spring furthest south along the fault.
Two heat-flow drill holes in the central part of the Black Rock Desert (within 4.8 km of Black Rock), which are not affected by the local movement of thermal groundwater, indicate that the heat flow in the Black Rock Desert area is probably not more than two heat flow units (HFU), which is not unusually high for the northern Basin and Range province (Olmsted and others, 1975).