Joaquin Miller is a little gem in Oakland with a bunch of legal and illegal singletrack. I recommend hitting up Sunset Trail for some great views, and one steep but short technical climb, then hitting Big Trees trail for some single track windies in the trees and finally, not for the weal at heart the illegal Palos Colorados Trail.
How to get there:
Best entrance is located by taking the PArk Blvd exit off Hwy 13 and then heading south on Mountain Blvd, take a right on Maountain gate and park. climb up the steep Castle Rd and take a right before the eucalyptus grove onto Sunet trail.