The Three Forks Loop is a strong-intermediate to advanced trail. Length is 16 miles, with 1900 vertical feet of elevation change. The trail begins at Three Forks, where Cottonwood Creek, Sixth Water, and Diamond Fork Creek come together. From the parking area, ride through the gate next to the rest rooms. Then immediately turn right onto a small footbridge that crosses Sixth Water. After crossing the river, bike straight ahead about 100 feet and plunge straight through Cottonwood Creek. Once you've crossed Cottonwood Creek, you're on the trail.
At 4.7 miles, the trail comes to a dirt road. The actual trail turns to the left a climbs sharply uphill. You can either follow the trail or cross the small stream and ride the dirt road - both will eventually connect to Ray's Valley Road. If you're a strong rider, take the trail (my preference). At the waterfalls, you'll have to carry your bike up a short rock face. At a trail intersection .5 miles above the waterfalls, turn to the right.
At Ray's Valley Road, turn left onto the road and ride 4.5 to 5 miles to the Fifth Water Trail. (Look for a prominent double-track crossing the road on the far side of a creek, note the sign that says "Fifth Water," and turn left downhill.) The first mile of Fifth Water is double-track. The next two miles of single-track have some tricky sections, then the trail widens and runs quickly down to Sixth Water (a larger creek), then to the Three Forks trailhead. You'll come out of the woods next to the bridge you crossed to reach Cottonwood Creek.