from the stickies above
HANDGUNS
California Penal Code section 12025 does not prevent a citizen of the United States over 18 years of age who is not within any of the classes excepted from firearm possession and who resides or is temporarily in California from transporting by motor vehicle any pistol, revolver, or other firearm capable of being concealed upon the person if the firearm is unloaded and in a locked container.
However since you are no longer a resident, you may have an issue with "importing" high-cap mags. If you had maintained residency, there would be no issues. Follow ALL the rules, and don't let the man into your life unnecessarily. In other words, don't carry concealed and get caught, etc etc.no traffic stops where the guns aren't being transported legally, etc etc
Don't be stupid, if you decide to go some place where you think you really need to carry because it is dangerous, re-start, re-think and don't go there.
you mention one following handgun, are you asking about handguns or rifles?