At 145°F, the source water at Upper Loon Creek Hot Springs is hot enough to cause burns. Some hot springs this hot have cooler side pools or downstream areas suitable for soaking — always test the water temperature before entering.
Upper Loon Creek Hot Springs discharges at 145°F with a strongly alkaline pH of 9.3 and sodium-dominant chemistry. Located on Challis National Forest land at 5,080 feet, it requires a 7-kilometer hike from Loon Creek Road, placing it firmly in backcountry-only territory. USGS-confirmed temperature: 65°C.
The spring sits deep in the Salmon River Mountains of Custer County, surrounded by steep, forested canyon walls along Loon Creek. At 5,080 feet, lodgepole pine and Douglas fir dominate the slopes. The creek drainage cuts through granite and volcanic rock formations, and the nearest maintained road, Loon Creek Road, ends well short of the spring. Average annual snowfall reaches 99 inches, burying the terrain from November through April. Annual precipitation totals 21.9 inches, keeping the area dry in summer.
History of Upper Loon Creek Hot Springs
The spring takes its name from Loon Creek, a tributary of the Middle Fork of the Salmon River. Historical records are sparse for this particular thermal feature, though the broader Loon Creek area saw mining activity during Idaho's late-1800s gold rush era. The spring remains undeveloped and managed by the US Forest Service within the Challis National Forest. No commercial infrastructure exists at the site.
Summer access only, typically July through September, after snowmelt clears the trail. Bring backcountry gear including water purification, bear spray, and overnight supplies for the long hike in. The nearest campground, Custer #1, is 28 km away and not reservable. Source water at 145°F is dangerously hot; allow it to cool before any contact. Check current trail conditions with the Challis Ranger District.
Is Upper Loon Creek Hot Springs worth visiting?
Best for
Observing powerful hot springs
Overnight camping trips
Not ideal for
Casual soaking
Upper Loon Creek Hot Springs is well suited for observing powerful hot springs and overnight camping trips.
Monthly Climate
25°Jan
27°Feb
34°Mar
39°Apr
47°May
58°Jun
69°Jul
68°Aug
58°Sep
44°Oct
31°Nov
23°Dec
Annual Precip: 21.9 inAnnual Snow: 99.0 in
Best Time to Visit
DecemberAir 23°F · Water 145°F · +123° contrast
JanuaryAir 25°F · Water 145°F · +120° contrast
FebruaryAir 27°F · Water 145°F · +118° contrast
December offers 47°F more contrast than July
USGS Field Measurements
Recent Temperature
149.0°F
(65.0°C)Measured Jul 30, 1979
Water ChemistrySampled 1979-07-30
The water at Upper Loon Creek Hot Springs is alkaline (pH 9.3).
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.
USGS Quad: ROCK CREEK 7.5 · PP 492: 56.0 · NOAA: 10.0 · AMS Map: CHALLIS
Frequently Asked Questions
What is the water temperature at Upper Loon Creek Hot Springs?
Upper Loon Creek Hot Springs has a water temperature of 145°F (63°C). This is considered a hot spring, well above body temperature.
Where is Upper Loon Creek Hot Springs located?
Upper Loon Creek Hot Springs is located in Custer County, Idaho at 5,080 feet elevation, near Challis. Coordinates: 44.6450°N, 114.7390°W.
How do I get to Upper Loon Creek Hot Springs?
Upper Loon Creek Hot Springs has Hike road access, with the nearest road being Loon Creek Road (4.5 mi from the road).
Is Upper Loon Creek Hot Springs free to visit?
Upper Loon Creek Hot Springs has Open access. It is managed by US Forest Service.
Can I camp near Upper Loon Creek Hot Springs?
Yes, Custer #1 Campground is located nearby (17.4 miles away).
What minerals are in the water at Upper Loon Creek Hot Springs?
Water chemistry analysis shows the presence of pH, Calcium, Magnesium, Sodium, Sulfate, Chloride. The pH is 9.3 (alkaline).
Is it safe to soak at Upper Loon Creek Hot Springs?
The water at Upper Loon Creek Hot Springs reaches 145°F, which can cause severe burns. Do not enter the source pool directly — look for cooled side pools or downstream areas where the water has cooled to a safe temperature. Always tell someone your plans before visiting remote hot springs.
Is Upper Loon Creek Hot Springs crowded?
Upper Loon Creek Hot Springs sees varying levels of visitors depending on the season and day of the week.
What should I bring to Upper Loon Creek Hot Springs?
Essentials for Upper Loon Creek Hot Springs: swimsuit, towel, water bottle, warm layers for before and after soaking, camping gear, a trash bag to pack out what you pack in. The water is over 110°F — test the temperature before entering and watch for scalding near the source.
Temperature
145°F
WarmHotBoiling
Water Temp145°F (63°C)
Avg Air Temp44°F
Above Ambient+101°F
Perfect soaking weatherMarch
Access
Open
Road AccessHike
Nearest RoadLoon Creek Road
Distance to Road4.5 mi
Land
OwnershipFederal
AgencyUS Forest Service
DesignationNational Forest
UnitChallis National Forest
ManagerUS Forest Service
Protection3 - Protected, subject to extractive use