In case you hadn't gathered yet, California is a pretty weird place.
So far as I can tell *, California Penal Code does not define 'concealed'. It says other things, e.g. PC 12025 " (f) Firearms carried openly in belt holsters are
not concealed within the meaning of this section."
The PC uses the word as if it were defined:
12025. (a) A person is guilty of carrying a concealed firearm when
he or she does any of the following:
(1) Carries concealed within any vehicle which is under his or her
control or direction any pistol, revolver, or other firearm capable
of being concealed upon the person.
(2) Carries concealed upon his or her person any pistol, revolver,
or other firearm capable of being concealed upon the person.
(3) Causes to be carried concealed within any vehicle in which he
or she is an occupant any pistol, revolver, or other firearm capable
of being concealed upon the person.
Definitions are in PC 12000, and again, it uses
concealed but does not seem to define it.
I do know that in
People v. Hale (1974) 43 Cal.App.3rd 353,356 a California Court of Appeals ruled that a firearm carried unloaded and completely openly on the seat of a car, magazine removed and
concealed made the whole weapon concealed. Makes me wonder who invented the phrase 'sober as a judge'.
Open carry is not specifically authorized by law (except as noted [by kungfuhippie] regarding the low-population counties) - it's just
not forbidden when UNLOADED; open, LOADED needs that variant CCW. Carrying loaded has restrictions; carrying concealed has restrictions; carrying open unloaded avoids both sets of restrictions, but is not explicitly allowed or disallowed.
So, in theory, Count Glockula, you should be able to carry open, unloaded, in an IWB not covered by a shirt or jacket or whatnot, up to the point where the range may say 'no holstered guns', if they choose that restriction. And before I tried that, I'd visit my personal lawyer for a sanity check.
I don't know
why you would do that. PC 12031 (e) says
(e) In order to determine whether or not a firearm is loaded for
the purpose of enforcing this section, peace officers are authorized
to examine any firearm carried by anyone on his or her person or in a
vehicle while in any public place or on any public street in an
incorporated city or prohibited area of an unincorporated territory.
Refusal to allow a peace officer to inspect a firearm pursuant to
this section constitutes probable cause for arrest for violation of
this section.
So, if you get stopped by LEOs you are likely to get a muzzle screwed into your ear while they disarm you and teach you the meaning of 'felony prone'. After they determine the weapon is unloaded, they might figure out that you are not breaking any gun transport law, but might also find something like 'disturbing the peace'. Officer Friendly might even be nice about it and just advise that open carry spooks the locals, and would-you-please-not-do-that. In most of California, I would bet against the latter reaction.
* 'so far as I can tell' means I've looked pretty carefully through the Penal Code, and I don't see it. It might be there and I missed it, it might be phrased in a way I did not expect, it might not be in the Penal Code, I might have a recurring brain cramp on the subject.