Most of this park is in Land Bank Status and it belongs to the EBRPD. However, there is a little known legal single track which is fun for a quick ride.
To get to the single track, go to the end of Brigadoon Way and make a left on Mc Bride. At the end of Mc Bride you will see a fire road on the right. Take that right turn, start climbing, and go threw the cattle gate. Continue on the fire road and it will turn to the right (next to a frog pond). Then you will climb a short steep section and make a right. (Note: You could also follow the game trail on the left, which will take you to a long fire road (~6 miles). Just watch out for aggressive cows.) Once you made the right turn, you will be on the single track, which takes you back to Brigadoon Way. Not great nor a destination but fun if you are local.
http://www.ebparks.org/parks/dublinh.htm
From I-680 southbound in San Ramon, take Exit 31, the San Ramon Valley Blvd. exit. Turn left on San Ramon Valley Blvd. San Ramon Valley Blvd. becomes San Ramon Road. Continue south to Dublin Blvd. and turn right (west). Continue west on Dublin Blvd. for two miles. The staging area is on the right. From I-680 northbound in Dublin, take exit 31, the Alcosta Blvd. exit. Turn left on Alcosta, and left again on San Ramon Road. Continue south to Dublin Blvd. and turn right (west). Continue west on Dublin Blvd. for two miles. The staging area is on the right. From I-580 eastbound or westbound, take exit 44A, the San Ramon Road/Foothil Road exit, and turn north on San Ramon Road/Foothill Road to Dublin Blvd. Turn west on Dublin Blvd. and drive for about two miles. The staging area is on the right.
http://www.singletracks.com/item.php?c=1&i=1314