Park at Half Moon Overlook/Sweeney Creek Road (FSR #746). Follow Sweeney Creek Road (FSR #746) for 0.8 miles, turn right onto FSR #744, cross Sweeney Creek, at the next road junction with FSR #744A continue right on #744, continue to the end of this road. Go left past the "no motor vehicle" sign and follow an old ATV trail. New re-route construction has begun about 1 mile beyond this point.
Ax of summer 2019, trail work is underway on several small re-routes on the Sweeney Creek Trail #121 (Grouse Mountain). Help ride it in, or better yet, ride it then stop for 30 minutes and kick loose rocks or rake some tread smooth. There's a rake on the side of the trail near the mini-excavator. Beyond the excavator, the trail quickly turns into hike-a-bike, but if you hike to the top, it's worth the view.
Trail work will continue into the fall, with additional re-routes and new switchbacks. New signage will also be added at each road junction starting from Skyline Drive.