For quiet your best bet is some of the BLM boondocking spots. Anza Borrego has spaces which are not closely packed.
Rincon Parkway north of Ventura is a first come first to get a spot boondock county campground that parallels the Pacific Ocean. The sound of the waves pretty much drown out any other noises except the trains that go by.
A little further north is San Lorenzo Park in King City (central Calif.) We liked it so much that an overnight stop turned into a 5 day stay. At the time several years ago there was a strong onion smell due to the farm fields nearby. But we got used to it. Spaces aren't closely packed, hook ups and big grassy areas. Nice agricultural museum on the grounds.
http://www.co.monterey.ca.us/parks/sanlorenzo.html
During the weekdays most RV Resorts in So Cal will have empty lots of empty spots except around holidays. Our favorite, Chula Vista RV Resort near San Diego pretty much empties out in the center pull through spots on Sunday and fills up again on Fridays. So we often will have no one on either side Monday through Thursday during the summer weeks.