East of Crested Butte, the Reno/Flag/Bear/Deadmans loop is an amazing 18 mile loop with several sustained 1,000 feet climbs (totaling 3,400 of vertical) and awesome rolling singletrack descents.
To reach the mountain biking trailhead from Crested Butte, head south on SR135 for seven miles to Crested Butte South. Turn left heading east on Cement Creek Road (FS740) for 6.5 miles to the Deadmans Trailhead parking area on the right.
Continue riding east up FS740 into the tight gorge along Cement Creek shaded by pine. After two miles and beyond the switchback, veer right up Reno Divide Road (FS759). For the next 3.5 miles, this moderate grade ascends through the conifers past an old homestead meadow with views of Double Top Mountain on the way to the pass at 11,100 . At the top, evaluate your water and power bar stash since the difficult stretch with two more climbs is ahead. A bail option here is to follow the forest road on the right before the gate which leads west to the top of Deadmans Gulch (thus bypassing those climbs and 90% of the singletrack!).
Pass through the gate and head down the Flag Creek Trail (#422). This singletrack starts at the headwaters and undulates through a narrow meadow between the pines as Flag Creek grows. After five wild miles, the Bear Creek Trail (#415) splits to the right crossing Flag Creek. Proceed 2 miles up a sustain climb through another meadow to the Bear Creek headwaters. At this cool bowl, climb up to a forest road and turn left. Proceed west on the road for about 0.75 miles to pick up the continuation of Bear Creek Trail on the right.
This is the best section of tight singletrack yet as it rolls four miles through meadows and pine forests, before dumping out at the barren hills of Deadmans Gulch. The DGT (#420) bears sharply right running up a narrow canyon squeezed by rolling hills. In many places, the gulch necks down to 20 feet wide before opening up again to reveal another lush valley created by generations of beaver dams.
After 3 miles of intense climbing on exposed trail, push the bike over the last ridge at the headwaters. Now, heres the best part of the mountain bike ride -- its a 1,500 descent down a mile through 30+ switchbacks. At the banks of Cement Creek again, head upstream to the log bridge, and take time riverside to revel in the magnitude of the adventure.
Overall, Reno-Flag-Bear-Deadmans is the 29th most popular mountain bike trail of all 176 mountain biking rides in Colorado.