Southwest of Boulder, the Walker Ranch Loop is a 7.4 mile loop through the Walker Ranch Open Space. While this is technically a multi-use trail system open to biking, hiking and horseback riding, it is ideal for mountain biking. Although it is heavily debated which direction is the best to ride this loop, for the first time try riding counterclockwise (i.e. take the right trail from the trailhead). Either way, youve got two awesome descents and two 600 feet vertical climbs. This ride offers great scenery and two bridged river crossings. Except for the burn area near the trailhead, there is a surprising amount of lush forest to traverse. The climbs can be real grunts, but are very doable with practice. Some of the climbing is exposed, so you may not want to do this ride mid-day in the summer. Also, weekends get very crowded, so try to do this really early, or on a weekday where you ll probably be the only one on the trail.
To reach the trailhead from downtown Boulder, head south on Broadway to Baseline Road. Turn right heading west on Baseline. As Baseline climbs, it turns into Flagstaff Road. Continue up Flagstaff Road for about 8 miles to the signed trailhead on the left.
Overall, Walker Ranch Loop is the 90th most popular mountain bike trail of all 175 mountain biking rides in Colorado.