Southwest of Moab, the 100-mile loop on the White Rim Trail in Canyonlands National Park has become revered as one of the finest multi-day mountain bike rides in the world. The trail clings to the precipitous canyon walls on narrow shelf roads, following the Green and Colorado rivers in a loop through the national park. The absolutely spectacular scenery along the trail can be enjoyed by cyclists of all abilities on a four-day supported tour. Careful pre-tour planning of equipment and food are mandatory. National Park Service personnel at the Island In The Sky Visitor Center can provide specific information on riding on The White Rim, or contact one of many Moab-based bike touring companies about guided tours. Note: the few campsites along the Rim are by reservation only and tend to be reserved many months in advance. Also, there is no potable water sources along the route so bring your own.
To reach the trailhead, follow US70 and exit at US191. Head south on US191. Turn southwest on SR313 for 22 miles into the park. The White Rim Trail, while called a loop, is actually more of a horseshoe shape. One end of the horseshoe is at the intersection with the Shaffer Trail (jeep road), which is located just past the park entrace on the left and requires descending 1,700 feet through narrow rugged switchbacks. The other end is at the end of Mineral Road (17 miles) (aka Horsethief Trail), which is located on the right about 5 miles before the park entrance. Both trailheads are remote.
While not recommended, there are many hardcore riders in Moab that do the entire loop (from town no less) in one day counting on water from local tour operators along the way. Only after you do the loop on a four day supported tour, then can you appreciate the magnitude of undertaking the route in one day.
Overall, White Rim Trail is the 4th most popular mountain bike trail of all 74 mountain biking rides in Utah.