To reach the trailhead leave Interstate 80 at Yuba Gap and take Hwy 20 towards Nevada City. After heading down for a few miles look for the Lake Bowman road on the right. Stay on the paved Lake Bowman road for a little over six miles until reaching the Grouse Ridge Lookout road. Although a little rocky, the un-paved Grouse Ridge Lookout road can be driven by any regular vehicle. Follow this dirt road for about 5.5 miles until reaching the primitive campground below the abandoned lookout. From the campground, which is situated near the top of Grouse Ridge, you can see Black Butte in the distance. It took us (my son and I) about two hours to hike to the mountain from here.
From the campground follow the trail along the northeast ridge downward for about 500 feet. At all trail junctions stay right until eventually hitting the Glacier Lake Trail. Follow the Glacier Lake Trail to where it nears Black Butte and before it drops down to the lake. Leave the trail here and head up the gully on the east side of the mountain (the gully on the west side also works but is more difficult). Once on the ridge circle around to the southern side of Black Butte and tackle the tricky class 3 moves to the top. There are good views from the summit, including Castle Peak, English Mountain, Sierra Buttes, and Interstate 80. No register was found. For additional reference see the English Mountain 7.5 quad map, and Pete Yamagata's Northern Sierra Peaks Guide.