Hospital Hot Spring
Hospital Hot Spring flows at 115°F deep in the Boise National Forest backcountry, requiring a genuine hike of over two miles from the nearest road. At 4,000 feet in Custer County near Challis, it rewards the effort with alkaline sodium-sulfate water carrying a total dissolved solids count of 278 mg/L and a pH of 8.9.
The trail to the spring crosses rugged terrain through mixed conifer forest in the Middle Fork country. The surrounding landscape is steep, rocky, and largely untracked, with few other visitors on most days. The Salmon River Mountains rise in every direction, and the drainage feels genuinely remote. Annual snowfall exceeds 100 inches, and the forest floor stays damp and mossy through early summer. The spring pools steam visibly in the cool mountain air.
The name Hospital Hot Spring likely references early use by miners or settlers who believed in the therapeutic properties of mineral water. The chemistry bears this out with distinctive alkaline characteristics: zero detectable magnesium, very low calcium at 3.4 mg/L, and dominant sodium at 90 mg/L. The Boise National Forest manages the surrounding area, which falls within the broader Idaho Batholith where deep crustal fractures bring heated water to the surface.
Yellowjacket Guard Station, a historic 1925 structure remodeled by the CCC in 1934, is the nearest reservable accommodation at nearly 30 miles. The spring sits over 3,400 meters from the nearest road, so plan for a serious hike. Bring sufficient water and navigation tools. At 115°F, source water needs substantial cooling before contact. This is not a casual day trip; plan for backcountry conditions and variable weather.
Is Hospital Hot Spring worth visiting?
Best for
- Hot spring soaking
- Overnight camping trips
The water at Hospital Hot Spring is alkaline (pH 8.9) with 278 mg/L total dissolved solids.
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Overview Yellowjacket Guard Station is a historic Forest Service Ranger Station and Work Center. Originally constructed in 1925 and remodeled in 1934 by the Civilian Conservation Corps, the structure is eligible for listing on the National Register of Historic Places. Recreation Hikers, horseback riders, mountain bikers and off-road enthusiasts will find many trails in the surrounding area. Hunting is also a popular activity. Click here for an Idaho OHV safety messageFacilities The spacious...