I can tell you this much, if you're thinking about going onto Corps of Engineers land (Knights Ferry, anyone?) or federal land, there are absolutely no guns allowed.
But in the state forests you can open carry. Also, in state forests, your campsite is considered your domicile and you can have weapons there.
Actualy that is the opposite of the truth.
State Parks and various forests are actualy off limits with severe penalties. Federal forests like National Forest are much more gun friendly.
BLM land is some of the most friendly to gun rights in the state, and that is also federal.
So the best land for gun rights, both national forests and BLM land are both federal.
While the absolute worst where it is a crime to even have a firearm inside them are State Parks and State Reserves, State monuments, etc
National Parks are also not firearm friendly, but are still more so than State Parks.
So clearly it is the Federal land that in general is far more gun friendly than State land.
For backpacking firearms rights are confusing. Many trails change from one territory to another. From a National Forest to a more restricted jurisdiction. So you need very detailed topo maps to stay legal, and the various agencies sell such maps for profit if you visit thier websites.
You generaly cannot just carry a firearm for self defense on most backpacking land. You can however carry one for "hunting". To legaly hunt you need to purchase a hunting license, and take a hunter's safety course.
What you are hunting changes the law on how many rounds you can legaly have in various types of firearms.
You can however legaly have any state legal firearm at your campsite in the state, as it becomes your legal temporary residence.
Your campsite is wherever you stop and setup camp while backpacking.
Technicaly it is legal to open carry an unloaded firearm without any license, even with ammunition on you. However some people have still had trouble with that as the police or prosecutors in some areas don't like what the law actualy says, and make up thier own version, so it is not advised.
CA law is relatively silent on legal transport of a long gun outside of a vehicle. For a pistol it must be unloaded. A pistol must also be in a locked case
if concealed.
"Assault weapons" as defined by CA law (which differs from the old federal definition of the term) cannot be brought into the state. Nor can magazines that hold over 10 rounds.
Varmint hunting with a rifle does not cap capacity so 10 rounds is legal (state maximum), but shotgun magazine capacity is capped lower for all hunting. Game hunting allows fewer rounds for both rifles and shotguns.
So your best bet is a rifle for varmints, and a hunting license.
Fees for a hunting license are:
Annual resident $38.85.
Junior annual resident hunting license is $10.25.
Non resident annual hunting license is $134.95.
Two-Day Nonresident license, age 16 and over (not valid for big game) $38.85.
Reduced Fee, Disabled Veteran $6.00.
Duplicate Hunting License $6.30 .
Hunter Education Stamp is $3.75.
You will have to take a CA approved hunter education course for your hunting license.
That really is the only way to legaly provide for protection from 2 and 4 legged predators while backpacking. Some CA mountains do have a lot of mountain lions, which are a protected species within the state (heavy jail time).
So to legaly provide for your protection you will need to purchase a lot of topo maps with clear legaly defined borders that show changes in jurisdiction. You will need to purchase a hunting license. You will need to then follow hunting laws and limits whether you choose to actualy hunt or not.
Totaly cost to excercise your RKBA in some portions of the state for your longer than 2-day stay will probably cost over $200.
Non resident annual hunting license alone is $134.95.
The topo map costs will vary depending on detail and total area.
If you need to purchase CA legal magazines, change features, or purchase a whole new CA legal firearm that adds up.
That is assuming you are going to be hiking where hunting is even legal. Many of the most beautiful parts of CA do not allow firearms at all.
Welcome to CA.