Bottom line:
Ordinary long guns (shotguns and rifles) can be transported in CA unloaded. It's perfectly legal to drive with an unloaded Rem 870 and a box of shells in the cab of your truck as a 'truck gun'.
Now, if any rifle is a semiautomatic centerfire with detachable magazine and has any other evil features (flash hider, pistol grip, folding stock, etc.) it's an assault weapon and is either illegal or must have been specially registered as such before 2000. Registered assault weapons have specific destination requirements for their transport and you can't cruise around with these like you can a Rem 870, Rem 700, ordinary Min14, etc..
Bans on loaded magazines only apply to street gang members. Nevertheless I feel that if you have loaded magazines you should have a separate empty magazine inside the firearm.
Oh - if a cop asks you why you are travelling with a shotgun, tell him it's because travelling with a pistol in your glove box is illegal.
Bill Wiese
San Jose, CA