Little Antelope Flat Warm Spring
Little Antelope Flat Warm Spring sits right beside the road near Challis at 93 degrees Fahrenheit -- warm enough to feel pleasant but not scalding. With a neutral pH of 7.4 and 130 milligrams per liter of sulfate, the water carries a distinctly mineral character that reflects its passage through Custer County's volcanic and sedimentary bedrock.
At 5,640 feet on a broad flat in central Idaho's ranching country, this spring emerges just 28 meters from the road. The landscape is classic Basin and Range: sagebrush, bunchgrass, and distant peaks still holding snow into June. The Pahsimeroi Valley stretches to the north, and the Lost River Range rises to the east. The mineral-rich water pools among grasses and sediment, with a faint sulfur note carried on dry air that averages only 15 inches of annual precipitation.
This is a roadside spring -- pull off and walk less than 30 meters. At 93 degrees, the water is comfortable for soaking without needing to cool it first. Herd Lake Campground is 33 kilometers away with one first-come, first-served site and a 14-day stay limit. Bring all supplies; this is remote country with no services nearby. The access road to the campground is narrow and difficult with trailers.
Central Idaho's thermal springs cluster along deep crustal fractures related to Basin and Range faulting and the track of the Yellowstone hotspot. The calcium-magnesium-sulfate chemistry here differs from the sodium-chloride signature of deeper-circulating springs, suggesting a shallower flow path through carbonate and volcanic rocks. USGS measurements confirm the temperature at 33 degrees Celsius, matching the historical 93-degree Fahrenheit reading from NOAA's 1980 survey.
The water at Little Antelope Flat Warm Spring is slightly alkaline (pH 7.4).
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Herd Lake Campsite is adjacent to Jerry Peak-Jim McClure Wilderness. There is one (1) first come, first served campsite located 10 miles southeast of the East Fork Road on Herd Lake Road. The site is located about 1 mile north of Herd Lake, tucked down below the road and next to Herd Creek. The access road to the campsite is narrow with limited turn-around space. Use caution with trailers. A trail provides non-motorized access to the lake. Amenities include: 1 campsite with picnic table and...
Little Antelope Flat Warm Spring sits at 5,640 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 23% stronger than at sea level, so bring sunscreen and drink more water than you normally would.
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Little Antelope Flat Warm Spring is road-accessible, so you can bring more gear. Cold air temperatures make a changing robe or warm layers essential.
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Springs Near Little Antelope Flat Warm Spring
More Springs Around 93°F
Slightly Alkaline Springs (pH ~7.4)
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