Sullivan Hot Springs
Sullivan Hot Springs surfaces at 106 degrees Fahrenheit right off the road near Challis, delivering a genuine soak temperature without any hiking required. The sodium-rich water carries 684 mg/L total dissolved solids, giving it a distinctly mineral character that separates it from nearby springs.
At 5,540 feet in Custer County, the spring emerges in sagebrush-covered terrain where the Salmon River drainage opens into wide valleys. The water has a faintly alkaline feel from its near-neutral pH of 6.9 and elevated sodium content at 170 mg/L. Steam rises more visibly during colder months when ambient temperatures drop well below the 42-degree annual average. The surrounding landscape is dry and open, with scattered cottonwoods marking nearby waterways.
Sullivan sits just 34 meters from the road, making it one of the easiest thermal springs to reach in Custer County. No formal facilities exist at the spring itself. Pole Flat Campground lies about 23 kilometers away and operates first-come, first-served with vault toilets and drinking water. Bring containers if you want to pack water from camp.
The spring taps into geothermal circulation along the Trans-Challis Fault System, where water descends thousands of feet before returning heated through fractured volcanic rock. Its 64-degree temperature differential above ambient air demonstrates substantial geothermal input. The calcium and magnesium concentrations suggest the water passes through both volcanic and sedimentary formations on its way to the surface.
The water at Sullivan Hot Springs is neutral (pH 6.9) with 684 mg/L total dissolved solids.
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This campground is away from the main road and up the hill overlooking the river and the dredge ponds. Campsites include picnic tables tent pads fire rings with cooking grills. Campground amenities include a vault toilet and drinking water. Sites accommodate trailers and motorhomes up to 32 feet long.
Sullivan Hot Springs sits at 5,540 feet above sea level, way above the mile-high mark. You may not feel the altitude strongly, but hot water still dehydrates you faster at elevation. UV is about 22% stronger than at sea level, so bring sunscreen and drink more water than you normally would.
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Sullivan Hot Springs is road-accessible, so you can bring more gear. Cold air temperatures make a changing robe or warm layers essential.
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