Mt. Diablo State Park From East Bay: Hwy 24 East to 680 North to Ygnacio Valley Rd. East; follow signs to Mt. Diablo State Park. Website: www.parks.ca.gov/default.asp?page_id=517Phone: 925 837-2525Mailing Address:98 Mitchel Canyon RoadClayton, CA 94517Date Updated: 2/18/2011