Getting Oriented
The Dusy-Ershim sits in Fresno County's Sierra National Forest, between two reservoirs that form the trailheads. Courtright Reservoir at the western end is accessed from Shaver Lake via Forest Road 9S09 and 8S03; Lake Edison at the eastern end is accessed from Mono Hot Springs via Edison Lake Road. The trail runs at the western edge of the John Muir Wilderness (one of the largest wildernesses in the lower 48), and most of the route's named features sit on the wilderness boundary.
The trail's name combines two early Sierra prospectors, Frank Dusy and J.A. Ershim, who used parts of the route in the 1880s.
Trail Overview
From Courtright Reservoir, the route climbs east through granite domes and lodgepole forest, reaching the trail's signature obstacle, Thompson Hill, within the first few miles. Thompson Hill is a series of large granite ledges with multiple line-choice options, none of them easy. Past Thompson, the trail eases through alpine meadow into the Helms Creek drainage, then climbs again to a series of high-elevation lakes (Lake 4, Lake 5, etc.). The eastern descent drops through Bear Diversion Dam to Lake Edison.
Most groups take 2 to 4 days to traverse the route, camping at the alpine lakes along the way. The route requires both technical 4WD skill and Sierra-backcountry preparedness; sudden weather, altitude, and remote-rescue limitations all come into play.
Points of Interest
- Thompson Hill. The route's hardest stretch, a few miles in from the Courtright end.
- Helms Creek. Mid-trail crossing.
- Lake 4 / Lake 5. Alpine lakes near the high-elevation midpoint with primitive camping.
- John Muir Wilderness boundary. Visible for most of the trail.
- Granite domes. Exposed-rock formations characteristic of the high Sierra.
- Lake Edison. Eastern terminus with developed campground and a small store.
- Mono Hot Springs. Natural hot springs near Lake Edison.
Where to Camp
Dispersed camping is allowed at the alpine lakes along the route with the standard wilderness regulations (free permits required for overnight camping in the wilderness portions). Courtright Reservoir and Lake Edison both have developed Forest Service campgrounds with fees. Pack out everything; the alpine ecosystem is sensitive to traffic damage.
Tips for a Safe and Enjoyable Trip
- Travel August through September. Snow blocks the route most of the year.
- Wilderness permits required for overnight camping inside the John Muir Wilderness.
- Travel in two or more vehicles. The trail's remoteness and altitude make recovery slow.
- Plan 2 to 4 days. Single-day attempts at the full 33 miles are unrealistic.
- Carry recovery gear, a full-size spare, and a winch. Body protection essential.
- Cell coverage is absent. Carry a satellite messenger.
- Acclimate to altitude before driving. The route reaches 10,000+ feet.
- Stay on the marked route. Off-trail driving in the alpine is illegal and damaging.
- Lightning hits the high country regularly. Plan to be off ridgelines by afternoon.
- Pack out all waste; alpine soils have no decomposition capacity.
- Contact the Sierra National Forest's High Sierra Ranger District at 559-855-5355 for current conditions.
