Fire roads and Cattle trails. The fun single track is actually the hiking trail. I've never seen hikers though.
How to get there:
from SF: 580 East toward Tracy/Stockton. Exit Vasco Rd. in Livermore, Head South. It will dead end, turn Right. Follow about a mile or two, Turn Left on Mines Rd. Follow about6 miles to park entrance. To avoid paying for parking, park at the top of the hill, before the park entrance and follow that trail. That is ridgeline trail.
I like to park at the top and follow ridgeline down the mountain and then ride the paved road back u