The trail starts at Storm Castle Rock/Garnet Mountain Trailhead. From your car, head across the bridge over Squaw Creek and start climbing on the singletrack that you'll eventually be flying down. It's an aesthetic climbing experience with a handful of very steep, technical sections, tight switchbacks, and obstacles to clear. Savor the views because you won't have much time to enjoy them on the downhill.
Once you end the singletrack, you can turn left and head up the old Forest Service Rd. to the lookout tower or you can turn around and let gravity take over. This climbing to the tower is very loose and will probably be more of a hike-a-bike than a good riding experience. The views are worth it, the riding is not.
The Forest Service rents the cabin out nightly, and it is well worth the experience.