Little Antelope Flat Warm Spring sits right beside the road near Challis at 93 degrees Fahrenheit -- warm enough to feel pleasant but not scalding. With a neutral pH of 7.4 and 130 milligrams per liter of sulfate, the water carries a distinctly mineral character that reflects its passage through Custer County's volcanic and sedimentary bedrock.
At 5,640 feet on a broad flat in central Idaho's ranching country, this spring emerges just 28 meters from the road. The landscape is classic Basin and Range: sagebrush, bunchgrass, and distant peaks still holding snow into June. The Pahsimeroi Valley stretches to the north, and the Lost River Range rises to the east. The mineral-rich water pools among grasses and sediment, with a faint sulfur note carried on dry air that averages only 15 inches of annual precipitation.
History of Little Antelope Flat Warm Spring
Central Idaho's thermal springs cluster along deep crustal fractures related to Basin and Range faulting and the track of the Yellowstone hotspot. The calcium-magnesium-sulfate chemistry here differs from the sodium-chloride signature of deeper-circulating springs, suggesting a shallower flow path through carbonate and volcanic rocks. USGS measurements confirm the temperature at 33 degrees Celsius, matching the historical 93-degree Fahrenheit reading from NOAA's 1980 survey.
This is a roadside spring -- pull off and walk less than 30 meters. At 93 degrees, the water is comfortable for soaking without needing to cool it first. Herd Lake Campground is 33 kilometers away with one first-come, first-served site and a 14-day stay limit. Bring all supplies; this is remote country with no services nearby. The access road to the campground is narrow and difficult with trailers.
Is Little Antelope Flat Warm Spring worth visiting?
Best for
- Warm-water soaking
- Easy day trips
- Overnight camping trips
Little Antelope Flat Warm Spring is well suited for warm-water soaking and easy day trips.
Annual Precip: 14.7 in
Annual Snow: 59.1 in
December
Air 19°F · Water 93°F · +74° contrast
January
Air 21°F · Water 93°F · +72° contrast
February
Air 23°F · Water 93°F · +70° contrast
December offers 52°F more contrast than July
Recent Temperature
91.4°F
(33.0°C)
Measured Apr 29, 1987
The water at Little Antelope Flat Warm Spring is slightly alkaline (pH 7.4).
pH influences mineral absorption through skin
May support bone density and joint health
Known for muscle relaxation and stress relief
Supports circulation and skin hydration
Traditionally used for skin conditions and inflammation
Natural antiseptic with skin health benefits
Herd Lake Campsite is adjacent to Jerry Peak-Jim McClure Wilderness. There is one (1) first come, first served campsite located 10 miles southeast of the East Fork Road on Herd Lake Road. The site is located about 1 mile north of Herd Lake, tucked down below the road and next to Herd Creek. The access road to the campsite is narrow with limited turn-around space. Use caution with trailers. A trail provides non-motorized access to the lake.
Amenities include: 1 campsite with picnic table and...
Reserve on Recreation.gov →
Swimsuit & towel
Water bottle
Stay hydrated, especially in hot water
Warm layers
Cold air before and after soaking
Camping gear
Nearby camping at Herd Lake Campground
Trash bag
Pack out what you pack in
37 miles from Challis, ID
USGS Quad: LITTLE ANTELOPE FLAT 7.5 · PP 492: 107.0 · NOAA: 13.0 · AMS Map: CHALLIS
What is the water temperature at Little Antelope Flat Warm Spring?
Little Antelope Flat Warm Spring has a water temperature of 93°F (34°C). This is a warm thermal spring.
Where is Little Antelope Flat Warm Spring located?
Little Antelope Flat Warm Spring is located in Custer County, Idaho at 5,640 feet elevation, near Challis. Coordinates: 44.3820°N, 114.0880°W.
How do I get to Little Antelope Flat Warm Spring?
Little Antelope Flat Warm Spring has Roadside road access (91 ft from the road).
Can I camp near Little Antelope Flat Warm Spring?
Yes, Herd Lake Campground is located nearby (20.4 miles away).
What minerals are in the water at Little Antelope Flat Warm Spring?
Water chemistry analysis shows the presence of pH, Calcium, Magnesium, Sodium, Sulfate, Chloride. The pH is 7.4 (slightly alkaline).
Is it safe to soak at Little Antelope Flat Warm Spring?
Little Antelope Flat Warm Spring is generally safe for soaking at its recorded temperature. Access may be on private land or unconfirmed — verify current conditions before visiting. Always tell someone your plans before visiting remote hot springs.
Is Little Antelope Flat Warm Spring crowded?
Little Antelope Flat Warm Spring is accessible from a paved road, making it easy to reach. Weekends and holidays may be busier — consider visiting on a weekday for a quieter experience.
What should I bring to Little Antelope Flat Warm Spring?
Essentials for Little Antelope Flat Warm Spring: swimsuit, towel, water bottle, warm layers for before and after soaking, camping gear, a trash bag to pack out what you pack in.