Upper Loon Creek Hot Springs
Upper Loon Creek Hot Springs discharges at 145°F with a strongly alkaline pH of 9.3 and sodium-dominant chemistry. Located on Challis National Forest land at 5,080 feet, it requires a 7-kilometer hike from Loon Creek Road, placing it firmly in backcountry-only territory. USGS-confirmed temperature: 65°C.
The spring sits deep in the Salmon River Mountains of Custer County, surrounded by steep, forested canyon walls along Loon Creek. At 5,080 feet, lodgepole pine and Douglas fir dominate the slopes. The creek drainage cuts through granite and volcanic rock formations, and the nearest maintained road, Loon Creek Road, ends well short of the spring. Average annual snowfall reaches 99 inches, burying the terrain from November through April. Annual precipitation totals 21.9 inches, keeping the area dry in summer.
Summer access only, typically July through September, after snowmelt clears the trail. Bring backcountry gear including water purification, bear spray, and overnight supplies for the long hike in. The nearest campground, Custer #1, is 28 km away and not reservable. Source water at 145°F is dangerously hot; allow it to cool before any contact. Check current trail conditions with the Challis Ranger District.
The spring takes its name from Loon Creek, a tributary of the Middle Fork of the Salmon River. Historical records are sparse for this particular thermal feature, though the broader Loon Creek area saw mining activity during Idaho's late-1800s gold rush era. The spring remains undeveloped and managed by the US Forest Service within the Challis National Forest. No commercial infrastructure exists at the site.
The water at Upper Loon Creek Hot Springs is alkaline (pH 9.3).
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This campground is along the Custer Motorway just above the townsite of Custer, a boom town during the late 1800's. Visit the museum, open 9 - 5 Memorial Day through Labor Day. Facilities include 6 sites with picnic tables and fire rings with cooking grills. Campground has a vault toilet and can accommodate trailers and motorhomes up to 32 feet long.
Upper Loon Creek Hot Springs is road-accessible, so you can bring more gear. The water is dangerously hot — bring water shoes and test pools carefully. Cold air temperatures make a changing robe or warm layers essential.
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