In the Pike National Forest, the Radical Hills / Swan River route is a 20 mile trek. It has great views and riding variety. It can be linked with Red Cone Road and Webster Pass Road for a huge loop.
To reach the trailhead from US70, take exit 205 toward Keystone. You will travel on Highway 6 through Dillon and Keystone, then take a right onto County Route 5 toward Montezuma. Continue through Montezuma on CR 5 until it meets Bullion Mine Road. Park here and begin the loop in either direction.
Note: Colorado residents must register their off-highway vehicle with the Colorado State Parks (303) 866-3437. Out-of-state residents who bring OHVs into Colorado must purchase a Colorado Non-Resident OHV permit which is valid from the date of purchase through the following March 31. These permits can be purchased anywhere you get your hunting/fishing licenses in Colorado. All off-highway vehicles must have an approved muffler and spark arrester. These requirements are subject to change so make sure to contact the Colorado State Parks prior to using your off-highway vehicle.
Note: As of September 2007, ATV riding on Forest Service roads is limited to designated roads that are signed as open or marked on the forest recreation map. To be safe (and legal), contact the Forest Service HQ to obtain a map at (719) 553-1400.