Red Warrior Creek Trail is a 30.2 mile loop trail located near Hailey, ID. The trail is rated as difficult and primarily used for mountain biking.
Hard to beat this ride. Although there is quite a bit of motorized and horseback travel around the Greenhorn Trailhead, these trails are nicely banked, well kept, with nice visibility. It's easy to link up some different routes, enough to spend a long weekend of 100% singletrack. I'd suggest dropping a few cars and camping from location to location, ie...out bottom of Red Warrior, South Fork of Warm Springs, and out Deer Creek Road.