Northwest of Fort Collins and Four Corners, there is a network of Forest Service roads open to dirt biking.
Note: Colorado residents must register their off-highway vehicle with the Colorado State Parks (303) 866-3437. Non-residents are not required to register in Colorado, if they are registered in their home states. 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.
Overall, Four Corners / Roach Road is the 82nd most popular dirt bike trail of all 93 dirt biking rides in Colorado.