Sutro Project / Tennessee Valley
Insulated by a 2 mile hike from the end of Tennessee Valley Road, the beach is a more secluded version of Rodeo Beach in the eye-popping Marin tradition.
The parking lot fills up on the busiest/nicest days, which makes for a longer walk along the road. It's a great area for bicycling (especially mountain) for those inclined.
Website: http://www.nps.gov/goga/planyourvisit/tennessee_valley.htm
Wikipedia: http://en.wikipedia.org/wiki/Tennessee_Cove
