Subsurface thermal observations indicate that Leach Hot Springs in Grass Valley, and Buffalo Hot Springs in Buffalo Valley, overlie localized upflows of hot water enclosed by relatively impermeable sediments. Upward and downward flows occur elsewhere in Grass Valley, probably indicating a complex system of hydrothermal circulation. The thermal data are inadequate to determine whether a comparable condition exists in Buffalo Valley. Deeper test drilling is being planned for both the Leach and Buffalo Hot Spring areas to find the depth to which the conductive regime extends and to provide further sub-surface data for an evaluation of the geothermal energy potential of the prospects.