 Gravity and seismic studies suggest that the source of heat for the steam reservoir is a large magma chamber over beneath the surface, and greater than in diameter.The first geothermal wells drilled in Geyser Canyon were the first in the Western Hemisphere.The first power plant at the Geysers was privately developed by the owner of The Geysers Resort and opened in 1921, producing 250 kilowatts of energy to light the resort.