Mammoth Hot Springs

The terraces are made of travertine, and the process behind them is simple to describe and remarkable to see. Rainwater and snowmelt sink deep into the ground, are heated by Yellowstone's underlying volcanic system, and rise again as hot springs. On the way up the water passes through thick beds of buried limestone and dissolves it, so it reaches the surface carrying dissolved stone. As that water spreads out and cools and loses its gas, it drops the stone back out as travertine, building the terraces higher, cup by delicate cup.

Because the plumbing underground shifts constantly, the springs are restless. New vents open and old ones seal, so a terrace that gushes and glows with color one season can turn dry and chalky gray the next. Some of the travertine near Gardiner formed tens of thousands of years ago, and older deposits on nearby Terrace Mountain are hundreds of thousands of years old, among the oldest hydrothermal deposits known in all of Yellowstone.

One of the strangest features stands at the base of the terraces: Liberty Cap, a lone gray cone about thirty-seven feet tall. It is the fossil throat of a hot spring that flowed for a very long time in one spot, slowly building a tower of travertine around itself before it finally went dry. Members of the 1871 Hayden Survey named it for its resemblance to the peaked liberty caps of the French Revolution, and it has stood as a landmark ever since.

The vivid oranges, browns, and greens that streak the wet terraces are not the stone itself but living things. Heat-loving microbes and bacteria thrive in the flowing water, each kind favoring a certain temperature, so the colors map out how hot the water is as it runs and cools down the terrace. Where the water stops flowing, the microbes die and the color fades to the bare white of the stone, another reason the springs look different on every visit.

The handsome buildings beside the springs tell a story most visitors do not expect. In the park's early years there was no agency to protect it, and poachers, vandals, and profiteers ran nearly unchecked. In 1886 the U.S. Army was sent in to bring order, and for about thirty years soldiers guarded Yellowstone from a post they built here at Mammoth. In 1891 that post became the permanent Fort Yellowstone, and at its height it housed a few hundred soldiers along with families and civilian staff.

The army enforced the rules, fought fires and poachers, and essentially invented the job that park rangers would later inherit. When the National Park Service took over in 1918 the soldiers left, but their fort stayed. Today more than thirty of those red-roofed stone and frame buildings survive as a National Historic Landmark district, now serving as park offices and housing, and elk often drift across the parade-ground lawns as if they own the place, which in a sense they do.

Mammoth is reached through Yellowstone's North Entrance at Gardiner, Montana, the park's only entrance open to cars year-round, so it makes a natural first or last stop. A network of boardwalks with stairs climbs among the lower and main terraces, an easy mile or two of walking, while the Upper Terrace Drive lets you see more formations from the car. Give yourself an hour or two to take it in slowly.

Stay on the boardwalks at all times, since the crust is thin and the water can be scalding, and keep a respectful distance from the elk and other wildlife that wander the area. Between the ever-changing terraces, the ghostly Liberty Cap, and the old fort with its grazing elk, Mammoth packs an unusual amount of Yellowstone, geology, wildlife, and history, into one walkable corner right above the town of Gardiner.

The closest Boutel™ stays, so you can turn this stop into an overnight. Each is an independently owned, editorially selected place to stay.