Yellowstone is a plateau high in the Rocky Mountains, and is snowbound for over six months per year. The mean annual temperature is 2.2°C (36°F), barely above the freezing point of water. However, Yellowstone is also an active geothermal area with hot springs emerging at ~92°C (~198°F) (the boiling point of water at Yellowstone's mean altitude) and steam vents reported as high as 135°C (275°F). Only about 0.3% of the park's terrain is thermal ground, so most places are no hotter than anywhere else in the Rockies.
In some of Yellowstone's thermal areas, heat flow is over 100 watts per square meter, about 50 times that of Yellowstone's average and ~2000 times that of average North American terrain. This enormous heat flow is derived from the molten rock or magma in the crust beneath the caldera, which ultimately is generated by the Yellowstone Hot Spot, an anomalously hot region of the Earth's mantle hundreds of kilometers beneath the surface.