Deadman's Gulch (Reno-Flag-Bear-Deadman's) is a 20.1 mile loop trail located near Crested Butte, CO that features a river and is rated as difficult. The trail is primarily used for mountain biking and is accessible from July until October.
Rather remote and solitary trail. I was one of only two bikers on this trail when I biked it.
It starts with a long steady climb (not technical) until you reach Reno Divide. Then some rewarding singletrack down, but you will pay for the descent. Bear Trail is one long climb on a singletrack. Technical enough to kick my butt (especially when combined with the climb). Climb continues on Deadman Trail for a while, testing me all the way to the top--and then fast and fun switchbacks all the way down. Last obstacle between me and my car was Cement Creek (which I ended up stepping into :))