Argentine Pass - Arapaho National Forest
Trail leading to 13,132 foot Argentine Pass for expert mountain bikers only. From Keystone take Montezuma Road 4.5 miles to Peru Gulch Trailhead. Follow Peru Gulch Trail for about 6 miles, then follow signs to Argentine Pass. Very rough, very steep terrain.
Breckenridge - Summit County
More than 200 miles of off-road trails. Ride the Superchair at Peak 8 to the top. From there, Peaks Trail winds along the eastern edge of the 10 Mile Range to the base. The portion of the Colorado Trail near Breck is an epic 26 mile loop. Follow Tiger Road out of town, go right at the first fork, head to Middle Fork at the next junction, then look for the trail on your left!
Hoosier Pass - Breckenridge
Follow State Route 9 on switchbacked, sometimes rough pavement for an elevation gain of 1900 feet in 11 miles as you climb to the summit of Hoosier Pass in the Arapaho National Forest.
Keystone - Summit County
Loaded with over 150 miles of awesome singletrack, lift access trails, a freeride park, and downhill trails, it's worth checking out. Let It Ride and Suz's Cruise are two favorites along with the new downhill trail: Motorhead (presumeably without the umlauts). Follow the West Ridge Loop of Keystone Gulch Road for six miles of great singletrack on the Colorado Trail.
Peaks Trail - Frisco
This 9 mile route connects Frisco and Breckenridge along the Tenmile Range.The trailhead in Frisco is at the intersection of I-70 and Main Street. Proceed south and turn right onto Rainbow Lake Road. The trail leads on past the lake and eventually into the Breckenridge Ski Area.