This post is to provide some additional information to what was posted on Tomales Bay.
The prior posting on Tomales Bay mentions Chicken Ranch Beach, which is a county park. This beach is just up the road (north) from Blue Waters Kayaks in Inverness. Just as you pass Blue Waters, watch for a porta-potty on the right side and pull out parking on the side of the road. This is the access to the beach. Parking is free, and I have left cars there overnight without problems.
You can camp on the beach at Marshall Beach, Tomales Beach, or any of the beaches north of there. Only Marshall and Tomales have pit toilets, so in the others you are supposed to, um, pack out your wastes.
If you camp on Marshall Beach or any of the beaches north of there, you will need to get a permit from the GGNRA.
Many useful contacts available from the previous Tomales Bay report.
Basic map online here.