Cosley Lake Trail

Cosley Lake Trail is a remote out-and-back from Chief Mountain Customs Trailhead to the shore and back, following the Belly River Trail before turning onto the Stoney Indian Pass Trail. Plan on about 17.6 miles round trip; descriptions put the lake about 8.7–8.8 miles from the trailhead, while the available mapped corridor measures about 9.2 miles one way. Treat that distance as an estimate and carry a map. Most visitors make this an overnight backpack; a same-day return is a very long day, roughly 10–11 hours depending on pace and stops.

The route drops roughly 700 feet over its first couple of miles through mixed pine and aspen, then levels out across open meadows, aspen groves and forest. It passes Gable Creek and reaches the Belly River Ranger Station area at about mile six. The valley section is gentler, but it is still a long way from the road in either direction.

Near the ranger station, take the Stoney Indian Pass branch and cross the Belly River on its suspension bridge. The trail climbs over a low ridge, then works through forest and meadow into the Mokowanis River valley before reaching Cosley Lake. The bridge is seasonal: Glacier’s trail guidance says most seasonal bridges are removed by late September, and early-season streams can run deep, fast and cold. Check current trail and crossing conditions before setting out.

Cosley Lake’s backcountry campground sits close to shore. Across the water, look for Pyramid Peak, Mount Kipp and Cathedral Peak; Shepherd Glacier lies on Cathedral Mountain’s slope, and Mount Cleveland appears in the wider view. Calm water can reflect the peaks. Overnight camping requires a wilderness permit and reservation; the 2024 campground map lists four sites, so confirm current arrangements before planning around a camp spot.

A short spur of about 100 yards reaches Gros Ventre Falls. Bear Mountain Observation Point is a separate, steep 1.7-mile spur that gains nearly 1,400 feet for a view over the Mokowanis valley. Neither spur is included in the Cosley distance or mapped route. The longer Stoney Indian Pass through-hike continues beyond the lake toward Goat Haunt; this row stops at Cosley.

The Belly River Ranger Station near the junction was built in 1925 and is listed on the National Register of Historic Places. It is a notable landmark along the valley approach, before the route leaves the Belly River corridor.

Use the Chief Mountain Customs Trailhead lot on the U.S. side, just before the border crossing; the hike does not cross into Canada. The trailhead source describes a large lot, but its capacity and overflow pattern are not established. No food, potable water or toilet stops were confirmed along the route, so treat Cosley as backcountry rather than a serviced campground. Dogs are not allowed on Glacier trails or in the backcountry.