Part of the Tongue River Shuttle route, you can access this trail off the Horse Creek Trail #159 as it shoots down into and through the canyon along Horse Creek. The western half is rarely accessed as it requires crossing the North Tongue River, which can be dangerous if not impossible.
The ride east from Horse Creek Trail #159 is surreal and steep. Squirm down it like a bucking cutthroat trout. Yeehaw! Near the end of the canyon includes some drop offs and some two-foot ledges to try and hop up. Falls might include rolling fifty feet into a whitewater river.
Lower parts of the trail include oodles of tourists. Check your speed. Give everyone else the right-of-way so bicyclists don't get banned from the trail.