Hot Springs
At 158 degrees Fahrenheit, this unnamed spring near Mountain Home runs far too hot for soaking but ranks among Elmore County's most thermally intense sources. It sits at 3,557 feet where the Snake River Plain meets rising foothills, its alkaline water carrying a pH of 9.4 and remarkably low calcium at just 0.4 mg/L.
The spring emerges in dry, open terrain typical of south-central Idaho's high desert transition zone, where sagebrush and bunchgrass cover the slopes. Annual rainfall barely reaches 15 inches, and winter brings light dustings of snow totaling around 32 inches. The air is dry and still. Steam rises visibly from the source, especially on cooler mornings when the 105-degree temperature differential between water and air is most pronounced.
The spring is a short walk of about 900 feet from the nearest road at 3,557 feet elevation. Water temperature makes direct contact dangerous. Spillway Campground on Anderson Ranch Reservoir sits 23 kilometers away and offers three first-come, first-served sites with fishing access for smallmouth bass and kokanee.
Geologically, this spring taps deep fracture systems along the northern margin of the Snake River Plain, where volcanic activity heated the underlying rock. The sodium-dominant, calcium-depleted chemistry and high pH point to prolonged contact with rhyolitic formations at depth. The 286 mg/L total dissolved solids suggest a moderately mineralized system with a long underground residence time.
The water at Hot Springs is alkaline (pH 9.4) with 286 mg/L total dissolved solids.
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Overview: Spillway Campground is a small campground with 3 campsites along Anderson Ranch Reservoir. The reservoir is a popular destination for fishing, boating, waterskiing and riding personal watercraft. There is excellent fishing in the reservoir for smallmouth bass and kokanee. Also try your luck at fly fishing just below the dam for a trout!Rafting access is at Reclamation Village, just south of the campground.
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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