Compilations of geologic and geophysical data from the Rio Grande rift indicate numerous geothermal anomalies, a few of which have been confirmed by subsurface temperature measurements. With the exception of anomalies associated with the Jemez Mountains, and possibly those near Socorro, there is no strong evidence to indicate that the anomalies are magmatic in origin. However, there is a strong correlation between the locations where the ground water discharges from one basin to the next, and the confirmed geothermal anomalies. A ground-water flow model, based on slow flow through the deeper basin horizons, explains the magnitude and distribution of the confirmed anomalies. Ground-water flow in the model is driven by the hydraulic gradients in the basins with no closed th rmal convection cells. Regionally high heat flow heats the ground water but the anomalies are located where the hot water rises naturally at the constrictions at the southern ends of the basins. The model indicates that intermediate to low temperature geothermal fluids may be encountered by deep (3 km) drilling in the basins, although low permeabilities at these depths may restrict production of fluids. It is more economically attractive to tap the flow systems where the hot water rises naturally at the basin constrictions. Data from two 300-m wells in the Las Alturas geothermal anomaly in south-central New Mexico are consistent with the ground-water flow model and indicate that near maximum temperatures may be reached at relatively shallow depths and deeper drilling may not encounter si nificantly higher temperatures.

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