Milford Sweat Hot Spring
Milford Sweat Hot Spring flows at 111 degrees Fahrenheit within Craters of the Moon National Preserve, one of the few thermal springs managed by the National Park Service in Idaho. Protected under the highest conservation status, this spring at 5,010 feet sits amid the lava flows and volcanic terrain that define this stark landscape in Blaine County.
A short walk of about 430 feet from Idaho Medal of Honor Highway leads to the spring, where warm water emerges through dark basalt in a landscape that looks more like the surface of the moon than typical Idaho rangeland. The surrounding lava fields absorb summer heat and radiate it back, amplifying the already warm 46-degree annual average. Precipitation is scarce at 13.4 inches per year, and 39 inches of snow highlights the black rock in winter with dramatic contrast.
The spring owes its existence to the same volcanic plumbing that created the Craters of the Moon lava field, where fissures and fractures in relatively young basalt allow groundwater to circulate near residual heat sources. USGS measurements show 42 degrees Celsius with a neutral pH of 7.0 and moderate mineral content. The preserve protects the Great Rift volcanic zone, which produced lava flows as recently as 2,000 years ago, and thermal features like Milford Sweat confirm that heat still moves through the system.
The spring sits within Craters of the Moon National Preserve, so all National Park Service regulations apply. Soaking or altering the spring is prohibited under the permanent protection designation. No campgrounds are listed in the immediate vicinity. The closest services are in Carey or Arco. Visiting between May and October avoids the heaviest snow. Bring binoculars for wildlife viewing across the lava fields, and stay on established paths to protect the fragile volcanic terrain.
Is Milford Sweat Hot Spring worth visiting?
Best for
- Hot spring soaking
The water at Milford Sweat Hot Spring is neutral (pH 7.0).