Really, the only way you could bring an AR (or other Calif.-designated A.W.) into Kalifornia is if you're going to a match that has been sanctioned by a recognized association (NRA, etc.) And I believe there's no exception for hicap mags.
...and that would be pretty much limited to going to/from said sanctioned match. Idling around in-state too much before or after could result in a bust - law is untested and murky, would you like to be the 1st test case?
So leave the AR at home. Bring a bolt gun, or Mini14 or M14/M1A with 10rd mags, or an SKS *without* detachable mag. [SKS' w/detach mag - even 10rnds! - are considered AWs by 1989 Roberti-Roos Act.]
BTW: while travelling thru Kalif with a handgun is indeed legal providing it's "safely" stored in your vehicle (unless you stay beyond, what is it? 60 days and are considered a 'personal handgun importer' and thus have to reg your handgun), this does NOT mean you can also bring in a hicap mag for your handgun. Federal pre/ postban hicap mag status is irrelevant here; noone can bring in new hicap mags except for existing residents who had theirs grandfathered (and who are allowed to travel in/out of state with them).
Like the other poster said, try to avoid spending $$$ in Kalifornia. It just feeds the liberalism.
Bill Wiese
San Mateo, CA