The direction of subsurface geothermal fluid flow before exploitation, and the geologic features controlling this movement were determined by integrating well completion and downhole temperature data with the geologic model. The data show that fluid (possibly heated by intrusive dikes found in wells drilled in the eastern area of the field) enters the system from the east at depths > 10,000 ft (>3,050 m). The fluid moves westward through sandstone beds and rises to shallow depths through fault zones and permeable sandy gaps in the overlying shale layers. Some of the hot fluid reaches the surface west of the field, in an area characterized by numerous geothermal manifestations. The rest of the fluid mixes with colder ground waters west of the geothermal resource.--Modified journal abstract.