Excellent hiking.
Exit I-680 at Ygnacio Valley Road in Walnut Creek and drive east. After about three miles turn right on Walnut Avenue. After about two miles turn right on Oak Grove Road, then bear right onto Castle Rock Road and follow it to the Orchard Staging Area on the right. Limited parking is available at the end of Castle Rock Road.
http://www.tripleblaze.com/trail.php?c=3&i=7347