Mammoth Hot Springs are a superficial expression of the deep volcanic forces at work in Yellowstone. Although these springs lie outside the caldera boundary, their energy is attributed to the same magmatic system that fuels other Yellowstone thermal areas. Hot water flows from Norris to Mammoth along a fault line roughly associated with the Norris to Mammoth road. Shallow circulation along this corridor allows Norris' super-heated water to cool somewhat before surfacing at Mammoth, generally at about 170 F.
Thermal activity here is extensive both over time and distance. Terrace Mountain, northwest of Golden Gate, has a thick cap of travertine. The Mammoth Terraces extend all the way from the hillside where we see them today, across the Parade Ground, and down to Boiling River. The Mammoth Hotel, as well as all of Fort Yellowstone, is built upon an old terrace formation known as Hotel Terrace. There was some concern when construction began in 1891 on the Fort site that the hollow ground would not support the weight of the buildings. Several large sink holes (fenced off) can be seen out on the Parade Ground. This area has been thermally active for several thousand years.
The Mammoth area exhibits much evidence of glacial activity from the Pinedale Glaciation. The summit of Terrace Mountain is covered with glacial till, thereby dating the travertine formation there to earlier than the end of the Pinedale Glaciation. Several thermal kames, including Capitol Hill and Dude Hill, are major features of the Mammoth Village area. Ice-marginal stream beds are in evidence in the small, narrow valleys where Floating Island Lake and Phantom Lake are found. In Gardner Canyon, one can see the old, sorted gravel bed of the Gardner River covered by unsorted glacial till.