Every hot spring on this site, plotted over a map of the heat rising through the ground. The warm colors mark where heat from deep in the earth reaches the surface fastest, and the springs crowd into them. 1,596 springs with heat flow data 102 median heat flow, mW/m² 1.6× the US average of 65 257 hottest ground, mW/m² Water Getting there Only Showing all 1,723 springs Tap a pin for the spring's water temperature and heat flow. Alaska and Hawaii springs are on the map without a heat flow value. Why Why Hot Springs Crowd Into the West Heat flow measures how much warmth works its way up from deep inside the earth, in milliwatts per square meter. Across the United States it averages about 65. Most of the West runs well above that. The crust there has been stretched thin and broken by faults, which leaves hot rock closer to the surface. Rain and snowmelt sink down through those cracks and come back up hot. The cool blue East has only a scattering of springs.…