Boulder Hot Springs
Boulder Hot Springs ranks among Montana's hottest natural thermal features at 169°F, confirmed by USGS measurement at 74.4°C. The water is strongly alkaline (pH 8.8) with sodium-dominant chemistry at 120 mg/L sodium and very low calcium (2.3 mg/L). It surfaces at 4,880 feet elevation in Jefferson County, 190 meters from the road.
The spring emerges in the Boulder River valley southeast of Helena, where the Elkhorn Mountains meet the northern edge of the Boulder Batholith. Rolling grassland and scattered conifer groves define the valley floor at this elevation. Annual snowfall averages 57.5 inches, and precipitation totals about 20 inches. The town of Boulder sits a few miles north in a broad intermontane basin. Radon-bearing granitic bedrock underlies much of the area, and the extreme water temperature reflects deep circulation through fractured plutonic rock.
Boulder Hot Springs has operated as a resort since the 1860s, making it one of Montana's oldest continuously used thermal sites. The current lodge building, constructed in stages between 1882 and 1920, is listed on the National Register of Historic Places. The property has functioned as a hotel, hospital, and retreat center at various points. The high sodium and low calcium chemistry produces soft, silky water that distinguished the resort from competing Montana hot spring destinations.
The spring itself is far too hot for direct contact at 169°F -- bathing occurs only in managed, cooled pools at the resort facility. Check current operating hours and reservation requirements before visiting, as the property has changed ownership and operating models multiple times. Boulder is accessible year-round via Interstate 15. The nearest reservable public campground is Sheepshead Picnic Area, 29 km away. Helena, 30 miles northwest, provides full urban services.
Is Boulder Hot Springs worth visiting?
Best for
- Observing powerful hot springs
- Overnight camping trips
Not ideal for
- Casual soaking
The water at Boulder Hot Springs is alkaline (pH 8.8).
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Overview Sheepshead Pavilion is available for reservations for private gatherings from mid-June through Labor Day weekend. The pavilion will accommodate about 200 people. It includes picnic tables, barbecue grills and water. There is no electricity to the pavilion, if electricity is needed please bring a generator. Fees are based on group size: $75 per day for groups 1-50 $125 per day for groups 51-100 $200 per day for groups 101-200 With a 2+ day reservation, overnight use may be granted,...