Trailhead is just inside the campground entrance. Stay on the Oats Peak trail (clearly marked) as all other trails south of Islay Creek are closed to mountain biking. This is an extremely well built trail that climbs for five miles. The last 1/2 mile is very steep with loose rocks. There is a wide turnaround point just before the final climb to the top.
Turn around and enjoy the 5+ miles of flowing downhill!