A few miles west of Cody, where the highway runs up the Shoshone River toward Yellowstone's east entrance, a pullout above the river looks down on a sulfur-stained bank, white ledges of travertine and a hot spring boxed into a pool. A state marker says this is Colter's Hell. Most people who know the name think it belongs to Yellowstone. It does not, and how it moved is half the story.
The name
John Colter left the Lewis and Clark expedition in 1806 to trap, and in the winter of 1807 and 1808 he set out alone from Manuel Lisa's new post at the mouth of the Bighorn to find the Crow and bring them in to trade. His exact route is argued over, but it took him up the river the trappers called the Stinking Water, now the Shoshone, past this canyon. Fur men of the 1820s and 1830s knew the steaming, sulfurous stretch here as Colter's Hell. The Jesuit Pierre-Jean De Smet placed it on the Stinking Water in the 1840s, and an 1867 Interior Department map marked a hot spring at Coulter's Hill near the forks of the Shoshone, well apart from the geyser basins.
The name traveled in 1895, when Hiram Chittenden, an Army engineer writing the first full history of Yellowstone, attached it to the park, and the tale of a trapper whose descriptions of the geyser country no one believed has been repeated ever since. The Park Service historian Merrill Mattes called it a case of mistaken identity. Colter may well have seen Yellowstone's thermal basins that winter, since the map William Clark drew from his account suggests he passed Yellowstone Lake. But the trappers' Colter's Hell was here.
The heat
This heat has nothing to do with the Yellowstone hotspot, or with the volcanoes that built the Absaroka Range and went quiet tens of millions of years ago. Geologists who have mapped the system describe ordinary groundwater warmed by depth. It soaks into limestone and sandstone beneath the Absarokas, works east and down through the folded layers, and rises where the river has cut through the fold of Rattlesnake Mountain. On the way it dissolves limestone and picks up sulfur, and where it reaches the air it drops calcium carbonate as travertine. The springs today run warm rather than hot, mostly from the 70s into the low 90s Fahrenheit, at DeMaris Springs on the north bank and a few vents upriver. The one the trappers seem to have remembered best, which an early visitor called a boiling tar spring, lies under the Buffalo Bill Reservoir.
The marker says Colter found an active geyser district, its eruptions now marked by cones of dry stone. Geologists disagree. The cones and terraces are travertine, which builds quickly and is too weak to hold the pressure a geyser needs; geysers like Yellowstone's build silica sinter, and none has been found here. What Colter saw was a field of hot springs, steam vents and sulfur, larger and livelier then than now.
What you see
Look across the river from the pullout and the history is in the cliff: sandstone stained orange and yellow by hot water that once moved through it, tilted beds of the Phosphoria Formation, and flat travertine laid down on top by springs. Charles DeMaris homesteaded the spring in 1888, before there was a Cody, and sold baths and bottled water; the bathhouse is long gone and the pool is private. Sulfur was mined here during the First World War, and a tunnel dug for the dam's water in the 1930s broke into caves that geologists think belong to the same system. The trappers' Colter's Hell has been cooling for a long time. It is still warm.