I usually just park at the Athenian School which is at the base of Mt. Diablo Scenic Blvd. (2100 Mt. Diablo Scenic. You turn left from Diablo Rd. to get to Mt. Diablo Scenic, and then it's your first right turn.) I guess it would depend on how many additional miles you want to do. [I get my fill just going up and down Diablo without the extra mileage.] There's a bunch of shops if you take Diablo Road and go west. Plenty of parking there too. Probably only 3 - 4 miles from the base of the climb. Also, you can take one exit further south on 680, Sycamore Valley Road, and go east which will take you into downtown Danville. Again, lots of shops and parking.