Yellowstone Hot Springs
Yellowstone National Park sits atop a geologically active supervolcano with magma bubbling so close to the surface, geysers and hot springs can reach burning temperatures. There are various geyser basins located where rainwater and snowmelt can percolate into the ground and then get superheated by the underlying thermal hotspots and erupt at the surface as geysers, hot springs, and fumaroles.
Thus flat-bottomed valleys between ancient lava flows are where most of the large geothermal areas are located such as Old Faithful and Grand Prismic Spring.