The Quantico Trails are located on Marine Corps Base Quantico. In order to access these trails, you will need to go through base security. Quantico is a very fun mountain bike trail. You can expect technical roots and rocks. These trails have short steep ascents and descents. Most of the traffic you will encounter is runners. There are 3 defined loops and the trails are well marked. Green - easiest, Yellow - Intermediate White - Advanced.