Foster Ranch Hot Springs
Four miles on foot from Sleeping Deer Road, Foster Ranch Hot Springs is one of the longer walks to a hot spring in Idaho on this site. It sits on Challis National Forest land in Custer County, roughly 23 miles from Challis. Hot water, mid 130s, and access listed as open. A photo is on record.
The trailhead on Sleeping Deer Road is where the driving stops. From there the hike covers about four miles into country that sits around 5,500 feet and collects close to nine feet of snow each winter, though outside the snow season it is on the dry side. Custer #1 Campground, about 18 miles off, is as close as developed camping gets, so nobody is camping at a trailhead facility here.
Midwinter, according to the best-months note, which on a four mile hike through nine feet of snow means snowshoes or patience until the melt. At 135 the water will burn; temper it first. The lab work is a 1979 sample that came back alkaline. The nearest listed campground is a long drive from the trailhead.
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 Foster Ranch Hot Springs.
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
- Canyon floor
- Steep ground climbs away on both sides of the spring.
- Highest ground nearby
- 850 ft above the spring
- Within a quarter mile, to the north
A slice through the ground from northwest to southeast, about 0.6 miles end to end.
Elevation data: USGS 3D Elevation Program. Aerial imagery: USGS The National Map. Public domain.
That's about 1½ times the US average of 65. It's higher than at 60% 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.
The water at Foster Ranch Hot Springs is alkaline (pH 9.1).
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This campground is along the Custer Motorway just above the townsite of Custer, a boom town during the late 1800's. Visit the museum, open 9 - 5 Memorial Day through Labor Day. Facilities include 6 sites with picnic tables and fire rings with cooking grills. Campground has a vault toilet and can accommodate trailers and motorhomes up to 32 feet long.
Foster Ranch Hot Springs sits at 5,520 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 22% stronger than at sea level, so bring sunscreen and drink more water than you normally would.
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Foster Ranch Hot Springs is road-accessible, so you can bring more gear. The water runs hot, so extra hydration is key. Cold air temperatures make a changing robe or warm layers essential.
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