The geothermal field at Roosevelt Hot Springs, Utah, produces water at temperatures exceeding 230 ¿C. The source of the heat for the geothermal field and the nature of the hydrothermal system have been investigated by analyses of gravity, thermal, and hydrogeologic data. A deep, cylindrically shaped, anomalous mass approximately 10--15 km in diameter is inferred to exist approximately 5 km beneath the geothermal field based on inverse modeling of a -17 mGal gravity anomaly isolated by strike filtering. This body is assumed to be a young intrusion and the heat source for the geothermal field. The configuration of the anomalous body was used in a vertical cross-sectional model of the hydrothermal system. The results of the modeling indicate (1) the source of the fluid recharge for the field is the Mineral Mountains; (2) the age of the source of the geothermal field may be younger than 500,000 years, the age of nearby rhyolites; (3) water at high temperature may be found beneath the sedimentary basin west of the geothermal field if sufficient permeability can be found; (4) the deep body beneath the field has significantly permeability, in excess of 5¿10-18 m2; and (5) the fault zone which acts as a conduit for upwelling thermal waters and provides the product at the field is probably bounded by low-permeability material. ¿ American Geophysical Union 1993