Sunflower Flat Hot Spring
Drag the handle to compare the two views. The orange dot marks the spring, in a frame about three quarters of a mile wide.
Sunflower Flat Hot Spring comes out at soaking temperature, around 109 degrees, on Challis National Forest ground, Custer County, about 42 miles from Challis. It is open to the public; count on a little under a mile on foot. A separate spring with a nearly identical name, Sunflower Hot Springs, appears in the same county and runs much hotter.
Around 4,500 feet, with ninety-eight inches of snowfall in an average year and about 22 inches of precipitation; mid forties is the yearly average. Forest Service acreage. Road to water is nine tenths of a mile on foot, and no road name is recorded. Beyond the National Forest label the record carries no designation.
Winter is the listed best season. Boundary Creek Campground, almost twenty miles out, is the closest camping on record. Water chemistry and temperature date to a June 1980 USGS sample, alkaline water in the soaking range. Check it with a hand before settling in, since the reading sits at the warm end of comfortable.
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 Sunflower Flat Hot Spring.
- Setting
- Canyon floor
- Steep ground climbs away on both sides of the spring.
- Highest ground nearby
- 659 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 twice the US average of 65. It's higher than at 74% 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 Sunflower Flat Hot Spring is alkaline (pH 9.2).
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Overview Boundary Creek Campground is located at the edge of the Frank Church River of No Return Wilderness, adjacent to the boat launch for the Middle Fork of the Salmon River in Idaho. The site generally provides overnight camping for boaters waiting to launch the next day on their permit to float the Middle Fork. Of the 15 campsites, 5 can be reserved during the high-use season (June 15-Aug. 15); the remaining 10 are first-come, first-served. Outside of those dates, all 15 sites are first-...
Sunflower Flat Hot Spring is road-accessible, so you can bring more gear.
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