Warm Springs
Warm Springs in Boise County flows at 108°F with a strongly alkaline pH of 9.5, the highest recorded among springs in this immediate area. USGS-confirmed at 42°C with sodium-dominant chemistry (65 mg/L sodium, 2.7 mg/L chloride). It emerges just 1.1 meters from the road at 3,850 feet elevation.
The spring surfaces along Mores Creek canyon on Highway 21, two miles south of Idaho City. At 3,850 feet, ponderosa pine and mixed conifers line the canyon walls while the creek corridor supports riparian vegetation including willows and alders. Annual snowfall averages 87.4 inches, moderate for the region, and precipitation totals 26.9 inches. The landscape reflects the area's gold-mining past, with exposed hillsides and remnant dredge tailings visible along the creek. The Boise Ridge rises to the west.
Highway 21 provides year-round paved access, making this one of the easiest thermal springs to reach in Boise County. Idaho City is two miles north with full visitor services including restaurants, lodging, and a museum. Grayback Campground is reservable and sits just 1 km away at the trailhead for the Grayback Loop Trail. Water at 108°F is hot but approachable. The area is 36 miles northeast of Boise, suitable for a day trip.
Idaho City, established in 1862 during the Boise Basin gold rush, was once one of the largest cities in the Northwest. The spring's generic name suggests it was a well-known local landmark rather than a formally named feature. Grayback Campground, 1 km away, provides a base along Highway 21. The Grayback Gulch Trail originates at the campground. The spring remains undeveloped, with thermal water flowing directly into the roadside drainage.
The water at Warm Springs is alkaline (pH 9.5).
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Overview Grayback Campground is located 36 miles northeast of Boise, Idaho, just off scenic Highway 21. Historic Idaho City is just two miles north of the campground. Visitors enjoy fishing in Mores Creek and exploring the Grayback Gulch Trail. Recreation Mores Creek can be accessed just below the campground. Anglers fish for whitefish and rainbow trout. Grayback Loop Trail begins within the site, offering a 1-mile footpath for hikers. Numerous trail opportunities are in the area just nort...
Warm Springs is road-accessible, so you can bring more gear.
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