California Code, Penal Code - PEN § 171e

A firearm shall be deemed loaded for the purposes of Sections 171c and 171d whenever both the firearm and unexpended ammunition capable of being discharged from such firearm are in the immediate possession of the same person.

In order to determine whether or not a firearm is loaded for the purpose of enforcing Section 171c or 171d, peace officers are authorized to examine any firearm carried by anyone on his person or in a vehicle while in any place or on the grounds of any place in or on which the possession of a loaded firearm is prohibited by Section 171c or 171d. Refusal to allow a peace officer to inspect a firearm pursuant to the provisions of this section constitutes probable cause for arrest for violation of Section 171c or 171d.