City and county park, it's the gateway to Annadel State Park. Good, short climbs for an after work work-out. Combinations fire trails and singletrack. Organized races every Wednesday evening in the summer.
From San Francisco, 101 north to Hwy 12 East exit; head east, cross Farmers Lane, continue to end of street (2miles) to Summerfield Rd. Left on Summerfield. Park entrance is 1/4 mile.
http://www.singletracks.com/item.php?c=1&i=1709