# Foster Ranch Hot Springs, Idaho

Foster Ranch Hot Springs in Idaho. 135°F (57°C). Hike · Public Land. Custer County.

- Page: https://www.soakingsprings.com/hot-springs/idaho/foster-ranch-hot-springs
- Source: Soaking Springs, researched and maintained by Armen Suny
- Updated: 2026-09-14

## Can you soak at Foster Ranch Hot Springs?

Only once it cools. The water leaves the ground at 135°F, hotter than any hot tub. Reaching it takes a hike. It's on US Forest Service land. We haven't confirmed whether it has a pool or charges a fee.

## Key facts

| Fact | Value |
|---|---|
| Source water temperature | 135°F (57°C) (USGS record; developed pools are often cooled) |
| pH | 9.1 (Alkaline) |
| Elevation | 5,520 ft |
| Access | Hike · Public Land, 4.0 mi from the nearest road (Sleeping Deer Road) |
| Land | Challis National Forest, US Forest Service |
| County | Custer County |
| Nearest town | Challis |
| Coordinates | 44.66100, -114.65200 |
| Best months to soak | December, January, February (largest gap between water and average air temperature) |
| Nearest campground | Custer #1 Campground, 18.1 mi |

## About 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.

## Water chemistry

Lab sample from 1979-07-30 (Water Quality Portal).

| Measure | Value |
|---|---|
| pH | 9.1 |
| Calcium | 2.5 mg/L |
| Sodium | 89 mg/L |
| Sulfate | 52 mg/L |
| Chloride | 9.9 mg/L |

## Nearby

- Nearest city page: [Hot springs near Challis](https://www.soakingsprings.com/hot-springs/near/idaho/challis), 29 mi away
- State page: [Hot springs in Idaho](https://www.soakingsprings.com/hot-springs/idaho)
- [Shower Bath Springs, ID](https://www.soakingsprings.com/hot-springs/idaho/shower-bath-springs): 122°F source, pH 9.3, Hike, near Challis, Custer County, primitive pools, free, jul-oct
- [Owen Cabin Hot Spring, ID](https://www.soakingsprings.com/hot-springs/idaho/owen-cabin-hot-spring): 133°F source, pH 9.3, Hike, near Challis, Custer County
- [Upper Loon Creek Hot Springs, ID](https://www.soakingsprings.com/hot-springs/idaho/upper-loon-creek-hot-springs): 145°F source, pH 9.3, Hike, near Challis, Custer County, primitive pools, pools 90–120°F, jul–oct
- [Lower Loon Creek Hot Spring, ID](https://www.soakingsprings.com/hot-springs/idaho/lower-loon-creek-hot-spring): 120°F source, pH 9.0, Short Walk, near Challis, Custer County, primitive pools, parking or permit fee, late may-sep (river permit season)
- [Cox Hot Springs, ID](https://www.soakingsprings.com/hot-springs/idaho/cox-hot-springs): 131°F source, pH 8.9, Hike, near Challis, Custer County
- [Hospital Hot Spring, ID](https://www.soakingsprings.com/hot-springs/idaho/hospital-hot-spring): 115°F source, pH 8.9, TDS 278 mg/L, Hike, near Challis, Custer County, primitive pools, parking or permit fee, late may-sep (river permit season)

## Questions

**What is the water temperature at Foster Ranch Hot Springs?**
Foster Ranch Hot Springs has a water temperature of 135°F (57°C). This is considered a hot spring, well above body temperature.

**Where is Foster Ranch Hot Springs located?**
Foster Ranch Hot Springs is located in Custer County, Idaho at 5,520 feet elevation, near Challis. Coordinates: 44.6610°N, 114.6520°W.

**How do I get to Foster Ranch Hot Springs?**
Foster Ranch Hot Springs has Hike road access, with the nearest road being Sleeping Deer Road (4.0 mi from the road).

**Is Foster Ranch Hot Springs free to visit?**
Foster Ranch Hot Springs has Open access. It is managed by US Forest Service.

**Can I camp near Foster Ranch Hot Springs?**
Yes, Custer #1 Campground is located nearby (18.1 miles away).

**What minerals are in the water at Foster Ranch Hot Springs?**
Water chemistry analysis shows the presence of pH, Calcium, Sodium, Sulfate, Chloride. The pH is 9.1 (alkaline).

**Is it safe to soak at Foster Ranch Hot Springs?**
With care. At 135°F Foster Ranch Hot Springs is hot enough to need short sessions, fifteen to twenty minutes, and plenty of water. Enter slowly and get out if you feel light-headed.

## Sources

- USGS thermal springs records, Water Quality Portal lab analyses, OpenStreetMap, Wikipedia/Wikidata, NOAA climate normals