Enter the forest and climb 0.2 miles, crossing an unpaved road servicing Bonneville power lines and a trail junction. Turn left and follow the road approximately 0.7 miles, crossing Alice Creek over an old a concrete culvert. A switchback and a climbing traverse ascend the embankment of the former Milwaukee Road Railroad, built in 1908 and abandoned in 1980. It is now part of the John Wayne Trail. Cross the John Wayne Trail at milepost 1.0 and continue up the trail, crossing Forest Service Road 9020 at milepost 1.9. Cross the road and continue.
The trail gets steep and switchbacks through woods revealing peak-a-boo views of the valley and surrounding peaks. At approximately milepost 4.5 cross a ridge to the west side of the peak and see views of the Cedar River Watershed and eventually Seattle and Puget Sound.
Traverse the west-facing slopes to a saddle and viewpoint just below the summit ridge at approximately 5.4 miles. The viewpoint at the end of the trail is a good place to stop and enjoy the scenery of the Snoqualmie Valley stretched out below. From the end of the trail, a short exposed scramble leads to the summit of McClellan Butte. Use extreme caution if you climb the rocks to the summit, they are slippery when wet and a fall could be fatal. via fs.usda.gov
Update from ACree:
Note: (technically) closed to bikes above the JWT. Definitely not a good MTB trail above the upper gravel road.