I called the PG Ranger station and they said it is a Motocycle single track from the Squaw Peak road up.
He said it goes over the mountain to Big Springs or "Something" Mill. He said it's a pretty tough trail.
I have a bike set up for low range single track so I'm not to worried, but....
Have you been over the mountain on it?
Are you talking about the Ridge Trail? That's trail #157. There's a parking lot at the top of the Alpine Loop and you can hop onto the trail right there. There are several intersections that take you different directions to other routes, not all are opened to motorcycles. You used to be able to ride down to Tibble Fork Res, which was a hell of a ride. The AF Canyon Field Office should have free maps of the trail system, you should familiarize yourself with the area then plot out a ride. The South Fork Deer Creek Trail is my favorite section up there, lots of rolling terrain that allows for a bit more speed. You can drop down to Cascade Springs and check that place out, if you like. I've been all over up there, ridden into Heber and back a couple times. It can be quite crowded on the weekends, if you can get up there on a weekday you will enjoy it soooooooooo much more.
The Ridge Trail will lead into Mud Springs, that would be one of the first intersections you hit. If you stay on the Ridge Trail you will eventually ride above Forest Lake. That section of trail gets SKETCHY on a motorcycle, ask Von.
If you drop your bike there, bail and just say buhbye.
The trail itself is amazing, depending on where you go it can be quite technical. Some of the upper portions can be quite rocky, with big roots crossing the trail and steep, loose climbs.
I have ridden in on a WR400 and a DRZ400 in the past, which was a good sized bike for those trails. Last year I rode it with Von, he was on his KTM450EXC-RWASDF or whatever and I was on my DR650. The 650 was too much bike for those trails, I got my ass kicked.
Here's a crappy map of the area-
Map and more trail info from-
http://www.utahmountainbiking.com/trails/ridge157.htm
I have some videos somewhere around here, I'll try to find them.