Overview
Mount Terrill is the high point of the Fishlake Plateau, topping out at 11,631 feet above sea level. The summit trail begins at a trailhead accessed via Forest Road 640 on the western plateau, already above 9,200 feet, which reduces the total driving-to-hiking elevation gain. From the trailhead, the route climbs steadily through spruce-fir forest before breaking onto open alpine tundra for the final approach. The summit delivers the widest views in Fishlake National Forest, with the Colorado Plateau stretching in every direction.
This is not a casual hike. The strenuous rating reflects the sustained grade on the upper section and the altitude. Hikers not acclimatized to elevation above 10,000 feet should plan extra time and pay attention to how they feel. The CDC and wilderness medicine resources recommend gradual acclimatization for sustained high-altitude activity.
The Route
Trailhead to Treeline (Miles 0-2.5) The trail departs from the Forest Road 640 pullout heading northeast along the plateau rim. The first 2.5 miles travel through old-growth spruce-fir forest, with occasional breaks in the canopy giving views west into the canyon country. The grade is steady but manageable. At around mile 2, the trees begin to thin and the slope steepens.
Treeline to Tundra (Miles 2.5-3.2) Above 10,800 feet, the forest opens into subalpine meadows and rocky tundra. Wildflowers, including phlox, alpine sunflower, and sky pilot, bloom here in July and early August. The views begin opening south toward the Henry Mountains. The trail becomes less defined on the tundra; cairns mark the route. Follow them carefully in fog or clouds.
Summit Approach (Miles 3.2-3.7) The final half-mile climbs over loose rock and tundra to the summit ridge. Wind is almost always present above the treeline, and strong gusts are common. The summit itself is marked by a USFS benchmark. On clear days, the panorama includes the Henry Mountains to the southeast, Capitol Reef's Waterpocket Fold to the east, the Tushar Mountains to the southwest, and Great Basin ranges to the west.
When to Hike
July is the best month: snow is gone from the upper route, wildflowers are at peak, and the days are long. Start before 7 a.m. to guarantee time on the summit before afternoon storms build.
August brings reliable afternoon thunderstorms, often arriving by 1 p.m. An early start is strongly recommended for safety on the exposed summit. The window between trail clear-of-snow and reliable afternoon storms is narrow in August.
September is excellent: fewer storms, cool temperatures, and fall color beginning on the lower slopes. The summit can get windy and cold; bring layers even on warm September days.
What to Bring
Many hikers carry 2.5 to 3 liters of water for this route, as there are no sources above the trailhead. A windproof shell, hat, and gloves are useful on the summit even in July. Trekking poles significantly ease the steep upper section on the return. Carry a map because cairns on the tundra can be hard to follow in reduced visibility. Review current conditions at /learn/checking-conditions-before-you-go before departing.
Trailhead Access
The trailhead is reached via Forest Road 640 off US-89 north of Antimony, Utah. The road is rough gravel; passenger cars can manage in dry conditions, but high-clearance vehicles are a practical advantage. No permit or fee is required as of 2026. Dogs are welcome on leash. No water or restroom is available at the trailhead. The access road typically opens in early July and closes with first heavy snow, usually October or November.
Nearby
For a less demanding summit experience, the Mytoge Mountain Trail climbs to good ridgeline views with significantly less elevation gain. The Thousand Lake Mountain Loop offers another high-plateau circuit on the south end of the forest. Follow Leave No Trace on the fragile summit tundra: /learn/leave-no-trace-7-principles.