Mammoth Hot Springs is a large complex of hot springs on a hill of travertine adjacent to Fort Yellowstone and the Mammoth Hot Springs Historic District.
It was created over thousands of years as hot water from the spring cooled and deposited calcium carbonate (over two tons flow into Mammoth each day in a solution). Although these springs lie outside the caldera boundary, their energy has been attributed to the same magmatic system that fuels other Yellowstone geothermal areas.
The hot water that feeds Mammoth comes from Norris Geyser Basin after traveling underground via a fault line that runs through limestone and roughly parallel to the Norris-to-Mammoth road. The limestone from rock formations along the fault is the source of the calcium carbonate. Shallow circulation along this corridor allows Norris' superheated water to slightly cool before surfacing at Mammoth, generally at about 170°F. Algae living in the warm pools have tinted the travertine shades of brown, orange, red, and green. Thermal activity here is extensive both over time and distance. The thermal flows show much variability with some variations taking place over periods ranging from decades to days. Terrace Mountain at Mammoth Hot Springs is the largest known carbonate-depositing spring in the world. The most famous feature at the springs is the Minerva Terrace, a series of travertine terraces. The terraces have been deposited by the spring over many years but, due to recent minor earthquake activity, the spring vent has shifted, rendering the terraces dry.