Thomas Creek Ranch Hot Spring
Thomas Creek Ranch Hot Spring delivers 138°F water on state-managed land in Custer County, requiring a short walk of roughly 244 meters from the road. With a pH of 9.3 and sodium-dominant chemistry at 86 mg/L, the water emerges from a deep-circulation geothermal system at 4,400 feet elevation on Idaho Department of Lands property.
The spring occupies a mid-elevation valley in central Idaho's rugged backcountry near Challis, where sagebrush benchlands transition into forested mountain slopes. The Middle Fork of the Salmon River drainage dominates the broader landscape. Annual snowfall reaches 98 inches, and average air temperature sits at 44.8°F, producing cold winters and short summers. The terrain around Thomas Creek is characteristic of Idaho's basin-and-range country — open rangeland cut by creek drainages flanked by steep ridgelines.
Access is best from late June through September, as winter snow and cold limit travel in this part of Custer County. The walk from the road is short but may cross uneven terrain. Water at 138°F is dangerously hot — do not enter without testing and mixing with cooler water. Boundary Creek Campground, about 31 km away, provides reservable sites near the Middle Fork Salmon River launch point.
The ranch in the name points to historical homesteading along Thomas Creek, though specific ownership records are not widely documented. The spring sits on a State Recreation Management Area under Idaho Department of Lands, indicating the state has formally recognized the site's recreational value. Custer County's hot springs were known to Indigenous peoples and later to ranchers and miners who settled the Salmon River country in the 1860s and 1870s.
The water at Thomas Creek Ranch Hot Spring is alkaline (pH 9.3).
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Overview Boundary Creek Campground is located at the edge of the Frank Church River of No Return Wilderness, adjacent to the boat launch for the Middle Fork of the Salmon River in Idaho. The site generally provides overnight camping for boaters waiting to launch the next day on their permit to float the Middle Fork. Of the 15 campsites, 5 can be reserved during the high-use season (June 15-Aug. 15); the remaining 10 are first-come, first-served. Outside of those dates, all 15 sites are first-...
Thomas Creek Ranch Hot Spring is road-accessible, so you can bring more gear. The water runs hot, so extra hydration is key. Cold air temperatures make a changing robe or warm layers essential.
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