An enclosed hot spring in Big Hole Valley, bubbling with hot water and spewing steam across the meadow, served as a late afternoon dinner stop on July 7, 1806, for Captain William Clark, Sacagawea, and their return party as they crossed this hot spring valley on the way to Camp Fortunate to retrieve canoes and supplies cached the previous summer. Clark wrote that the spring, about 100 paces from a large easterly fork of the small river that heads in the snowy mountains to the southeast and southwest of the springs, boiled up all over its stony bottom, held a very considerable quantity of water, and blubbered with heat for 20 paces below where it rose; meat placed in the water by Sergt. Pryor and John Shields cooked in 25 and 32 minutes. In 1833, fur trapper Warren Angus Ferris and his small company visited the site and wrote that Indians had made a succession of little dams from the upper end to the river, creating baths of every temperature from boiling hot to the river's water, which was too cold for bathing in any season. The hot springs reflect the region's geothermic activity, where a fault system dropped Big Hole Valley and raised the surrounding mountains, and fractured rock in the earth's crust allows water to percolate deep underground, be heated, and rise to the surface as a hot spring.