Sunflower Hot Springs
Sunflower Hot Springs delivers 149-degree water in the Boise National Forest, far too hot to enter at the source but capable of feeding soakable pools where it cools downstream. At 103.3 degrees above ambient air temperature, the geothermal input here is substantial and persistent.
An 867-meter walk through Custer County forest at 4,375 feet reaches the spring where it emerges from fractured rock. The pH of 9.3 makes the water feel notably smooth. The surrounding terrain is dry canyon country with scattered conifers and exposed granitic outcrops. Steam from the source is visible from a distance, especially in morning hours when cool air settles in the drainage. The landscape carries the open, arid character typical of central Idaho's middle elevations.
The source water at 149 degrees Fahrenheit causes serious burns. Only enter downstream pools where temperatures have dropped to safe levels. Test with a thermometer before soaking. The 0.5-mile approach is straightforward but unmarked. Boundary Creek Campground is the nearest reservable option at 32 kilometers. This spring pairs well with a visit to Sunflower Flat Hot Spring nearby for a comparison of the same thermal system at different temperatures.
Sunflower Hot Springs and nearby Sunflower Flat spring tap the same deep thermal system, yet emerge at dramatically different temperatures, with this source running 40 degrees hotter. Both carry alkaline, sodium-dominant water with minimal magnesium, pointing to shared circulation through Eocene volcanic deposits. USGS measurements confirmed 66 degrees Celsius. The two springs sit less than half a mile apart, offering a rare chance to compare related thermal features.
The water at Sunflower Hot Springs 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-...
Sunflower Hot Springs is road-accessible, so you can bring more gear. The water is dangerously hot — bring water shoes and test pools carefully.
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