This trail starts out from the Indian Creek campground/parking area. Just past the gate at the western end of the lot is the Indian Creek trailhead. Follow this trail up about .7 miles to an intersection of a dirt road and two singletrack trailheads, one of which you just ascended. A 'Ringtail' sign clearly marks the trailhead opposite you on the east side of the of intersection.
After entering the trail, you'll ascend for about 1 mile, until hitting a high point. From here it's 95% downhill. The trail get looser and a little narrower as you descend, and there are a few switchbacks near the bottom.
When you reach the bottom, you'll be at the Swallowtail trailhead, which is part of Nelson Ranch Open Space.