Rattlesnake Hot Spring

Boise County, Idaho · Near Idaho City
43.6050°N, 115.6640°W · 4,216 ft
133°F 35°F air · Good soaking weather 4,216 ft Open Hike US Forest Service Camping nearby (11.1 mi)
Aerial view of the ground around Rattlesnake Hot Spring LiDAR bare-earth view of the same ground around Rattlesnake Hot Spring
Aerial LiDAR bare earth

Drag the handle to compare the two views. The orange dot marks the spring, in a frame about three quarters of a mile wide.

Boise National Forest land holds Rattlesnake Hot Spring, in Boise County, 17 miles or so beyond Idaho City. The water is hot, near the upper end of what will cool to a soakable temperature. Access is open to anyone. No sample was ever taken and no USGS number assigned, which leaves the temperature as the one solid thing known about this water.

Location

A hike of a bit over a mile in from a road the record leaves nameless. Forest Service land at moderate elevation. Snow totals are moderate too, around four and a half feet, and the year is fairly dry with a cool average.

Big Roaring River Lake Campground, eleven miles out, is the camp on file. Winter, per the record. The water is hot enough to hurt, so find a cooled spot before you sit. With no chemistry to go by, you are relying on your own senses. The walk in is a little over a mile, so this is a hike, short as it is.

Terrain

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 Rattlesnake Hot Spring.

Setting
Canyon floor
Steep ground climbs away on both sides of the spring.
Highest ground nearby
466 ft above the spring
Within a quarter mile, to the south
Cross-section through the spring

A slice through the ground from south to north, about 0.6 miles end to end.

Elevation data: USGS 3D Elevation Program. Aerial imagery: USGS The National Map. Public domain.

Heat Below
125 milliwatts per square meter of heat flow

That's about twice the US average of 65. It's higher than at 75% 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.

Heat flow estimate: Stanford Thermal Earth Model (Aljubran & Horne, 2024), CC BY 4.0.

Monthly Climate
26°
Jan
29°
Feb
36°
Mar
43°
Apr
53°
May
62°
Jun
73°
Jul
72°
Aug
62°
Sep
47°
Oct
35°
Nov
25°
Dec
Annual Precip: 21.0 in Annual Snow: 53.6 in
Best Time to Visit
December Air 25°F · Water 133°F · +108° contrast
January Air 26°F · Water 133°F · +107° contrast
February Air 29°F · Water 133°F · +104° contrast
December offers 48°F more contrast than July
Current Conditions
35°F
Good soaking weather
Today 71° Low 48° Sunny
Spring is +62° warmer
Wednesday 77° Low 52° Sunny
Spring is +56° warmer
Thursday 70° Low 47° Showers And Thunderstorms Likely 67% precip
Spring is +63° warmer
Friday 71° Low 46° Sunny then Slight Chance Rain Showers 15% precip
Spring is +62° warmer
Saturday 74° Low 48° Sunny 4% precip
Spring is +59° warmer
Nearby Camping
Nearby Camping
Big Roaring River Lake Campground 11.1 mi away

Overview:  Set within the beautiful Trinity Recreation area, the Big Roaring River Lake Campground has12 campsites in a dense lodgepole forest on the river.The Trailhead to the north follows the Upper Roaring River and the Trailhead to the south accesses the William H. Pogue National Recreation Trail and the Lava Mountain Trail.Both trails are open to two-wheeled ATVs, horses, bikes, and people. The Lava Mountain Trail itself passes three lovely lakes on its way south to Lava Mountain.Fishing...

Reserve on Recreation.gov →
Temperature
133°F
Warm Hot Boiling
Water Temp 133°F (56°C)
Avg Air Temp 47°F
Above Ambient +86°F
Great soaking conditions September
Access
Open
Road Access Hike
Distance to Road 1.1 mi
Land
Ownership Federal
Agency US Forest Service
Designation National Forest
Unit Boise National Forest
Manager US Forest Service
Protection 3 - Protected, subject to extractive use
Frequently Asked Questions
What is the water temperature at Rattlesnake Hot Spring?
Rattlesnake Hot Spring has a water temperature of 133°F (56°C). This is considered a hot spring, well above body temperature.
Where is Rattlesnake Hot Spring located?
Rattlesnake Hot Spring is located in Boise County, Idaho at 4,216 feet elevation, near Idaho City. Coordinates: 43.6050°N, 115.6640°W.
How do I get to Rattlesnake Hot Spring?
Rattlesnake Hot Spring has Hike road access (1.1 mi from the road).
Is Rattlesnake Hot Spring free to visit?
Rattlesnake Hot Spring has Open access. It is managed by US Forest Service.
Can I camp near Rattlesnake Hot Spring?
Yes, Big Roaring River Lake Campground is located nearby (11.1 miles away).
Is it safe to soak at Rattlesnake Hot Spring?
With care. At 133°F Rattlesnake Hot Spring 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.