Begin on the north side of the Grassy Lake Road near the Flagg Ranch Information Station, the same location as the start of the Polecat Creek Loop Trail. Take the east (right) side of the loop and travel north 0.5 mile to the junction marked with a temporary sign. Turn right (east). The trail crosses the groomed snowmobile trail--use caution and watch for snowmobiles and snowcoaches. The marked trail continues on the east side of the road and leads to the Flagg Canyon Trail, which follows the Snake River. To reach the boundary of Yellowstone National Park, turn left (north). Use caution and avoid cornices where the trail follows the edge of the cliff above the Snake River. The trail ends at the groomed snowmobile trail--be alert for snowmobile and snowcoach traffic. To reach the South Gate of Yellowstone, turn right (north) and ski/ snowshoe 0.3 mile on the snowmobile trail; sometimes a ski trail may be broken on the east side of the snowmobile trail. Additional trails lead north and west from South Gate. Check at the South Gate ranger station for trailhead locations and conditions. Return to Flagg Ranch on the same trail or by taking the snowmobile trail.The Flagg Canyon Trail can also be reached from the north side of the Snake River bridge near Flagg Ranch's riverside motel units. Ski/snowshoe on the east side of the highway to the Snake River, then follow the trail along the river north for 1.2 miles to join the trail from Flagg Ranch. This section of trail is at river level for a short distance, then climbs on to the bench above the river.The Flagg Canyon trail affords spectacular views of cliffs composed of rhyolite, volcanic rock that flowed from Yellowstone about 600,000 years ago, lining the west side of the canyon. In winter the Snake River hosts waterfowl, especially Barrow's and common goldeneye ducks and Canada geese. Bald eagles often perch on snags above the river. Look and listen for dippers, small gray birds that favor rocky stretches of the river where they search underwater for insect larvae adhered to rocks. River otters occasionally cavort in the Snake River and otter slides may be seen on the snowy banks of the river.

Trailhead is located directly across from Flagg Ranch in the John D. Rockefeller Jr. Memorial Parkway (Hwy 89).

The terrain is gently rolling with a few short steep sections that can easily be avoided. This trail is also host to many types of wildlife, and hosts skiing and other winter activities.