A thermal study was made across a 25 km (15.5 mi) traverse of the Overthrust belt in southwestern Wyoming. Estimates of relative heat flow from temperature measurements made in shallow (< 30 m or 98 ft) boreholes reveal a systematic variation of at least 400 mW/m² (10 µcal/cm² sec) magnitude across the study area. The cause of this variation is believed to be forced convection of heat by moving ground water. Two relative heat-flow highs coincide with zones where structurally related faults, possibly providing avenues for vertical water flow, project to the surface. Between those two zones in a topographically elevated area, low and predominately negative temperature gradients were observed in opposite seasons. These shallow negative gradients are believed to exist seasonally in quasisteady state and could be indicative of a broad zone of ground-water recharge. The association of two relative heat-flow highs with the two major deep geologic structures implies either a direct vertical communication of deep and shallow ground water or a coupling of deeper and shallower ground-water systems. The two structures studied are hydrocarbon bearing and associated with Whitney Canyon and Ryckman Creek fields. The thermal measurements support the possibility that ascending waters have influenced the hydrocarbon migration and accumulation in these structures. Such measurements may be useful in delineating and understanding similar features in other areas.