Ninemeyer Hot Springs
Ninemeyer Hot Springs reaches a scalding 169°F along Middle Fork Road in Boise National Forest, making it one of Idaho's hottest accessible thermal features. Just 440 feet from the road at 3,760 feet elevation near Idaho City, it runs a staggering 120 degrees above the local average air temperature. Direct contact with the source is dangerous.
The spring emerges in the Middle Fork Boise River canyon, where steep, forested walls channel the drainage through Boise County's rugged interior. The canyon receives over 30 inches of rain and 10 feet of snow annually, feeding dense stands of Douglas fir and ponderosa pine. Steam rises visibly from the source in cooler months, and mineral deposits stain the surrounding rock. Ninemeyer Campground sits just 650 feet away, though a recent wildfire has stripped it of amenities including developed fire rings.
USGS measurements confirm source temperatures of 76°C with a pH of 9.6, among the most alkaline thermal waters in Idaho. The chemistry reads like a textbook deep-circulation system: calcium nearly absent at 1.6 mg/L, magnesium effectively zero, and sodium dominant at 64 mg/L. These signatures indicate water that has traveled miles underground through the Idaho Batholith's granitic rock before reaching the surface along Middle Fork faults.
The spring is a short walk from Middle Fork Road (Forest Road 268), but the 169°F source water causes severe burns on contact. Observe from a safe distance. Ninemeyer Campground is steps away but currently has no amenities due to wildfire damage and no fires are permitted during Stage 1 restrictions. The road is accessible by car in good weather from mid-May through late September but can be rough. Bring all supplies.
Is Ninemeyer Hot Springs worth visiting?
Best for
- Observing powerful hot springs
- Overnight camping trips
Not ideal for
- Casual soaking
The water at Ninemeyer Hot Springs is alkaline (pH 9.6) with 245 mg/L total dissolved solids.
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Overview:Due to a wildfire, there are no amenities at the campground. Currently there are no developed campfire rings therefore when Stage 1 fire restrictions area in effect, no fires are permitted.A stay at Ninemeyer Campground enables guests to enjoy all the beauty and recreation offered along the (Middle Fork Boise River Road) Forest Service (FS) Road 268. Weather is usually good from mid-May through late September and is easily accessible by car in good weather, although the road is some...