This is the main trail into the Happy Jack trail system from the Summit trailhead Parking area. A short climb to the highest point of the trail offers a great view of Happy Jack (especially in the fall). Then it's a not too technical descent all the way to the Headquarters parking area.
You can also ride this one from the Headquarters parking area. This will offer a pretty grueling climb with some tough rock/root sections.
Make sure you have a good idea were you're headed, or bring the MTB Project mobile app with you, as this trail intersects with other trails.