Rosalys Warm Spring
Rosalys Warm Spring surfaces at 106 degrees Fahrenheit and 6,560 feet elevation near Sun Valley, one of the higher-altitude thermal features in the state. Its pH of 9.4 makes it among the more alkaline springs in Idaho, with just 2.7 mg/L calcium dissolved in the water.
Reaching the spring requires a walk of roughly a quarter mile from the nearest road. The terrain sits in Blaine County high country where annual snowfall averages over 13 feet and the mean air temperature hovers around 39 degrees. The landscape is open and exposed at this elevation, with views across sagebrush meadows toward distant peaks. The mineral-laden water feeds a modest flow into the surrounding drainage.
The strongly alkaline chemistry and extremely low calcium suggest the water circulates deep through silicic volcanic rock, stripping sodium and sulfate while leaving calcium behind. At 6,560 feet, the spring occupies terrain shaped by Pleistocene glaciation and subsequent erosion. Outlet Campground near Redfish Lake, about six miles away, anchors the Sawtooth National Recreation Area that defines this stretch of central Idaho.
Access requires a short walk from the road, roughly 1,500 feet. Snow buries this area from late fall through spring, so plan visits between June and October. The nearest reservable campground is Outlet Campground at Redfish Lake, about six miles out. Water temperature is comfortable for soaking without mixing, though conditions vary seasonally.
Is Rosalys Warm Spring worth visiting?
Best for
- Hot spring soaking
- Overnight camping trips
- Winter soaking with dramatic temperature contrast
The water at Rosalys Warm Spring is alkaline (pH 9.4).
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Overview Outlet Campground is located next to beautiful Redfish Lake beneath the Sawtooth Mountain Range at an elevation of 6,500 feet. Recreation Outlet Campground is in the heart of the beautiful Sawtooth National Recreation Area, where outdoor activities abound. Redfish Lake offers excellent boating, water skiing, canoeing, kayaking and fishing for rainbow trout and Kokanee salmon. Little Redfish Lake is just down the road, offering additional fishing and canoeing. In the immediate are...