Overview
Eight Mile Mountain is the main summit objective in the southern portion of Boise National Forest, rising above the South Fork Boise River and the Anderson Ranch Reservoir. The 8-mile round-trip gains 2,400 feet from a trailhead that starts significantly lower than the northern forest routes, which makes the total climbing feel substantial despite the familiar distance.
The mountain's name reflects its location above Eight Mile Creek, one of the tributaries that drains this portion of the Boise Mountain terrain into the South Fork Boise River below. The creek provides water for the lower trail, and its canyon forms the corridor of the lower approach.
The summit view is the primary reward: Anderson Ranch Reservoir is clearly visible to the north, and the South Fork Boise River canyon stretches in both directions. The Owyhee Mountains appear on the horizon to the south in clear conditions. The view provides a compelling overview of the varied terrain that defines this part of southern Idaho, from the mountain forests of the Boise National Forest to the high desert of the Snake River Plain below.
This is a trail that rewards early starts, both for the light and the temperature. Summers in the South Fork Boise River corridor can be hot, and the lower trailhead elevation means temperatures at the start can be in the 80s by mid-morning in July and August.
Check current fire conditions before visiting. The South Fork Boise River corridor is in a high-fire-risk zone and trail closures due to fire or post-fire restrictions are not uncommon in late summer.
The Route
Miles 0 to 2.0: Eight Mile Creek Canyon
The trail begins at approximately 4,800 feet and follows Eight Mile Creek northeast into the canyon. The lower section runs through ponderosa pine and Douglas fir forest, with the creek visible and providing shade on the east-facing slopes. The gradient is moderate and consistent.
Ponderosa pine is the dominant tree at this elevation, giving the lower approach a distinctly different character from the lodgepole and spruce forests of the northern forest. Mule deer are common in this terrain, particularly in the morning.
Miles 2.0 to 4.0: Upper Approach
Above mile 2, the trail steepens and the forest transitions to lodgepole pine and eventually subalpine fir. The creek becomes intermittent and then absent above mile 2.5. Views begin to open on the upper slopes, with the reservoir visible to the north by mile 3.
The final mile is the steepest, climbing through open terrain to the rocky summit. Cairns mark the upper route where the trail is less distinct.
When to Visit
June through October. Early starts are strongly recommended in July and August to beat the midday heat at lower elevations. The summit clears of snow by mid-June in most years.
What to Bring
Many hikers on this route carry:
- 3 liters of water given the potential for high temperatures at the lower elevations; individual needs vary considerably based on conditions
- A water filter for the creek sources
- Sun protection for the open upper trail
- Layers for the summit, which can be windy even in summer
- Trekking poles for the steep sections
Practical Details
No permit required as of 2026. No trailhead facilities. Cell service absent. Dispersed camping permitted in the national forest. Dogs allowed on leash.
Leave No Trace principles apply throughout.
Getting There
From Mountain Home, drive northeast on Highway 20 to the Anderson Ranch Road junction. Take Anderson Ranch Road north toward the reservoir, then continue east on South Fork Boise River Road. The Eight Mile Creek Trailhead is signed off the South Fork road. Total drive from Mountain Home is approximately 1.5 hours on a mix of paved and dirt road. Check road conditions with the Mountain Home Ranger District before visiting.