Mammoth Hot Springs is a large complex of hot springs on a hill of travertine in Yellowstone National Park 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).

Because of the huge amount of geothermal vents, travertine flourishes. Although these springs lie outside the caldera boundary, their energy has been attributed to the same magmatic system that fuels other Yellowstone geothermal areas.

Mammoth Hot Springs has two terrace boardwalks, the upper and lower. Approximately 50 hot springs lie within the area. 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.

According to en.wikipedia.org; yellowstonepark.com. Source of photos: internet