In addition to Morro Bay there is great state park that is a few miles north of the town of Cambria and just south of a beach with elepant seals and the Hearst Castle.
For Xmas I would much rather stay in Tehachapi at the private RV park that is situated near the glider airport above the town.
Wherever you go in California I would phone ahead an confirm that they have water. With the ongoing drought some of the campgrounds have shut off the water.
Until the drought ends we do our camping in Idaho or Colorado (avoiding the red zone).