This information is taken directly from he State of California Department of Justice Attorney General website:
Transporting Firearms in California
HANDGUNS
Pursuant to California Penal Code section 25610, a United States citizen over 18 years of age who is not prohibited from firearm possession, and who resides or is temporarily in California, may transport by motor vehicle any handgun provided it is unloaded and locked in the vehicle’s trunk or in a locked container. Furthermore, the handgun must be carried directly to or from any motor vehicle for any lawful purpose and, while being carried must be contained within a locked container.
Pursuant to California Penal Code section 16850, the term “locked container” means a secure container that is fully enclosed and locked by a padlock, key lock, combination lock, or similar locking device. This includes the trunk of a motor vehicle, but does not include the utility or glove compartment.
SHOTGUNS AND RIFLES
Nonconcealable firearms (shotguns and rifles) are not generally covered within the provisions of California Penal Code section 25400 and therefore are not required to be transported in a locked container. However, as with any firearm, nonconcealable firearms must be unloaded while they are being transported.
REGISTERED ASSAULT WEAPONS
California Penal Code section 30945, subdivision (g) provides that registered assault weapons may be transported only between specified locations and must be unloaded and stored in a locked container when transported.
Pursuant to California Penal Code section 16850, the term “locked container” means a secure container that is fully enclosed and locked by a padlock, key lock, combination lock, or similar locking device. This includes the trunk of a motor vehicle, but does not include the utility or glove compartment.
It is important to follow the law on this one. AR rifles need to be in a lock box,