Grandjean Hot Spring
You can pull up to Grandjean Hot Spring without walking anywhere. It sits in Boise County, forty miles out of Idaho City. The ground belongs to the Boise National Forest and the public may use it. Listed as hot, with no temperature attached, so there is no degree reading to give here. Nobody sampled the water either. A photo exists, and a USGS site number. Not much else.
Under sixty feet from an unnamed road at five thousand feet. Snow is the big number here, better than fifteen feet a winter, and the year is moderately wet. Bonneville campground is around seven miles away and is the only camping the record lists. Nothing says what the pull-off or the spring looks like.
no season is on record. Temperature is unknown, so no soaking promise. It is a drive-up when the road is open, and with that snowfall the road is the thing to ask about. Bonneville campground for the night. Forest Service land, and the record marks access open.
Aircraft with laser scanners measured this ground to within inches. The scan strips out trees and buildings, leaving the bare shape of the land around Grandjean Hot Spring.
Drag the handle to compare the two views. The orange dot marks the spring, in a frame about three quarters of a mile wide.
- Setting
- Hillside
- The spring sits on a steep slope that climbs to the northeast.
- Highest ground nearby
- 595 ft above the spring
- Within a quarter mile, to the northeast
A slice through the ground from southwest to northeast, about 0.6 miles end to end.
Elevation data: USGS 3D Elevation Program. Aerial imagery: USGS The National Map. Public domain.
That's about twice the US average of 65. It's higher than at 90% of the springs on this site.
Heat flow measures the warmth working its way up through the ground from deep inside the earth. Where it runs high, rain and snowmelt that seep down through cracks in the rock come back up hot.
See every spring on the geothermal heat map →
Heat flow estimate: Stanford Thermal Earth Model (Aljubran & Horne, 2024), CC BY 4.0.
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Overview Bonneville Campground is 19 miles east of Lowman, Idaho just off Highway 21 at an elevation of 4,700 feet. Warm Springs Creek runs alongside the campground and the South Fork Payette River lies across the highway. Visitors enjoy soaking at Bonneville Hot Springs a short distance above the campground, and fishing in the creek and river.Recreation A 1/4-mile hiking trail leads from the campground to Bonneville Hot Springs, where a soaking pool awaits. Warm Springs Creek offers good tro...
Grandjean Hot Spring is road-accessible, so you can bring more gear. Cold air temperatures make a changing robe or warm layers essential.
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