California State Parks are not RV friendly in general. The vast majority have no hookups, small sites, low branches, and some forbid dogs, even just being in a vehicle. And for all that they charge high prices. (I say this as a disgusted California native.)
However, California also has many national parks, national forests, BLM land, regional parks, county parks, city parks, and of course private parks. If you are OK with dry camping, most truck stops allow it overnight, and it is generally legal to spend the night ("8 hours") at a freeway rest stop. However, most Walmarts do not allow overnights due to local regulations. And more than a few cities, especially along the coast, don't let RVs park in the best areas because local residents don't like it.
If you ignore the bone-head State parks there's still plenty of sights and camping to do in California.