Warm springs and wells 10 km northwest of Moapa are at the head of the Muddy River (figure) and have reported temperatures that average 32°C. Peterson Spring, a well near Home Ranch and Warm Spring all measured 32.2 °C; Iverson Spring measured 31.6 °C; C. Lewis Well measured 23.7 °C; and Woodruff and Perkins Well measured 27.5°C (Reed and others, 1982, p. 38). Mariner estimated the reservoir temperature to be 47°C (Mariner and others, 1982, p. 47).The springs issue from alluvium but probably are supplied by water that is transmitted through Paleozoic carbonate rocks which crop out nearby. Preliminary analysis of minor long-term spring discharge variations suggest a 15- to 20-year lag in response to recharge from precipitation (Eakin and Moore, 1964). The water at Iverson's Warm Springs has been used for irrigation and bathing (Eakin, 1964).