The state has a condensed guide to firearms laws. It might be a good idea if really concerned to check back against the references
https://oag.ca.gov/sites/all/files/agweb/pdfs/firearms/pdf/cfl2016.pdf
Note page 7 and thereabouts covers much of what you are interested in. Except for the "it's legal except for where it isn't legal" sort of language. I've lived in Ca pretty much all my life and never had any kind of inkling that this is a problem - that is, traveling or camping with guns. What you won't see in most, any?, organized campsites are people packing. So if you don't stand out, it's just unlikely to be an issue. Strap on a hogleg in a state park campground "Because this is the way we do it in New York City!" and you might get some negativity. They don't search cars at borders, don't ruffle through your gear or trunk entering state parks, etc. I don't really recall them even asking at any state or federal parks for years, if at all. There are some areas where theft from unoccupied vehicles could be a problem, usually isolated parking areas and they are usually signed.
I do some living history and a group wanted to go Old Town San Diego dressed old west for the fun of it and I reminded them that it was a state park, to not go heeled (even unloaded) and the dummies did. I didn't because, I really thought everyone knows you don't carry guns in state parks. The interpreter showed up pretty quick (Interpreters aren't rangers, not LEOs, do history, nature programs, etc.). It was clear what his issue was. He introduced himself as an Interpreter and smart-ass me asked him "What languages?" I showed him I wasn't wearing anything under my frock coat. Uh, wasn't wearing gun leather or shooting irons, that is. And then stepped away to watch the fun. All he did was given them a semi-stern talking to and made them put everything back in their cars. No arrests, no citations, no blood in the streets.