Pierson Hot Springs
Pierson Hot Springs pushes 109-degree Fahrenheit water roadside at 6,900 feet elevation near Ketchum, Idaho, in the heart of Sawtooth country. The alkaline water registers a pH of 9.3 with very low calcium and magnesium, producing a distinctly silky feel. USGS readings of 42 degrees Celsius confirm the source temperature remains stable.
Valley Road passes within 77 meters of the spring, placing it in easy reach against a backdrop of serious mountain terrain. The Sawtooth and Boulder ranges stack up to the west and north, their peaks often snow-covered well into June. At this elevation, annual snowfall averages over 13 feet, and the mean air temperature sits at just 38 degrees Fahrenheit. The spring emerges amid a narrow valley floor where lodgepole pine and Douglas fir crowd the drainage. The contrast between cold mountain air and warm water creates visible steam on most mornings.
Alturas Lake Picnic Area sits 8 kilometers away and accepts reservations. Roadside access via Valley Road keeps the approach simple. Source water at 109 degrees Fahrenheit is hot but generally soakable without mixing in cooler conditions. The Sun Valley area offers extensive services in Ketchum, roughly a short drive south. Winter access depends on road plowing schedules.
The geothermal source taps into the Idaho Batholith, a massive Cretaceous granite intrusion that underlies much of central Idaho. High pH, elevated sodium, and minimal calcium suggest the water circulates through granitic rock at depth, dissolving silica rather than carbonates. Blaine County's thermal features cluster along major fault intersections. The area saw intensive gold and silver mining in the 1880s, and miners used several local hot springs for washing and comfort.
The water at Pierson Hot Springs is alkaline (pH 9.3).
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Overview Alturas Area Picnic B is located along the sandy shoreline of scenic Alturas Lake, at the foot of the Sawtooth Mountain Range.Recreation The site is part of the Sawtooth National Recreation Area, where outdoor activities abound. Alturas Lake offers excellent boating, water skiing, canoeing, kayaking and fishing for bull trout and Kokanee salmon. Alturas Creek runs through the adjacent campground. The 10-mile round trip Alpine Meadows Trail begins nearby, with spectacular canyon, mea...
Pierson Hot Springs sits at 6,900 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 28% stronger than at sea level, so bring sunscreen and drink more water than you normally would.
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Pierson 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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