Rather than ride the singletrack portion that goes to the Big Pines Visitor center, I drove up the Blue Ridge Road. The road was open to vehicles past the Blue Ridge Campground, but the gate was closed at Guffy Campground. I parked at Guffy Campground and started riding from there.
After about a mile or so, you reach a fork in the road. The "high road" is 3N06, which continues parallel to the Pacific Crest Trail and provides access to the Acorn Trail and eventually dead ends near Wright Mountain. The "low road" is 3N39, which goes about 2000' down to Lupine Campground. I took the high road.
Close-up of the turnoff to the "high road", 3N06
Close-up of the turnoff to the "low road", 3N39
After continuing on 3N06, it can be a little tricky to find the turnoff to the Acorn Trail. Here's some views of the approach to the trail.
Here's the sign showing the start of the Acorn Trail. It's a little hard to find.
Close-up of the sign in the previous picture
Here's a picture going down the Acorn Trail. This is the trail that drops about 2000 feet in about 2 miles down to the town of Wrightwood. Notice how the trail switchbacks.