Check this website. It shows all the campground in SoCal.
http://www.trails.com/trailfinder/browsebymap/?statecode=CS&lat=34.642247&lon=-118.66333&z=7&m=terrain&a=CP
http://www.trails.com/trailfinder/browsebymap/?statecode=CS&lat=34.642247&lon=-118.66333&z=7&m=terrain&a=CP