East of Moab, the Porcupine Rim Trail is a extremely rugged, rocky 14 mile (one-way) route. This rugged route mainly follows rocky double track with 1,200 feet of climbing and 2,900 feet of descent. The best part of the route is the last three miles of pure singletrack with views over the Colorado River canyon.
The full route leads from Sand Flats Road to SR128 along the Colorado River. The trail follows an old, narrow jeep trail. It starts with a rocky scramble ascent of 500 feet over a couple miles, before leveling off to rolling terrain. There are canyons edge views into little-visited Negro Bill and Rill Canyons. Along Porcupine Rim, elevations are as high as 6,800 feet (900 feet above the trailhead and 3,000 feet above Moab), and vistas are superb in all directions. 1,500 feet below is Castle Valley with its prominent buttes, Castle Rock, Priest and the Nuns, and Round Mountain. Farther away are the Colorado River canyon, the Book Cliffs and features in Colorado. The La Sal Mountains are nearby, and a look to the west reveals parts of Moab and surrounding canyons.
There is much sandy dirt, some loose sand, and oodles of rock in various forms. Although there is some slickrock, most encounters are with bedrock poking through in knob. Because of its elevation, the trail occasionally has some snow or residual mud in the spring. Watch out for a fork in the trail at 8.5 miles: the right route leads to Mat Martin Point (4.5 mi. away) if you continue to stay to the right, while the left route leads to Jackass Canyon (2.5 mi. away). The jeep road, if you could call it that, end above Jackass Canyon. There is a narrow trail open to hikers and mountain bikers leading down Jackass Canyon to Negro Bill Canyon Parking area on SR128 at the Colorado River (about 5 miles back to town).
To reach the mountain biking trailhead for Porcupine Rim Trail from Moab, head east on Center Street. Turn right on 400 East and left on Mill Creek Drive. At Sand Flats Road, veer left and drive for 8.3 miles while looking for trailhead on left.
Overall, Porcupine Rim Trail is the 4th most popular mountain bike trail of all 74 mountain biking rides in Utah.