From the CAL DOJ site regarding dealers....
(2) As used in this section, a "secure facility" means a building that meets all of the following specifications:
(A) All perimeter doorways shall meet one of the following:
(i) A windowless steel security door equipped with both a dead bolt and a doorknob lock.
(ii) A windowed metal door that is equipped with both a dead bolt and a doorknob lock. If the window has an opening of 5 inches or more measured in any direction, the window shall be covered with steel bars of at least 1/2 inch diameter or metal grating of at least nine gauge affixed to the exterior or interior of the door.
(iii) A metal grate that is padlocked and affixed to the licensee's premises independent of the door and doorframe.
(B) All windows are covered with steel bars.
(C) Heating, ventilating, air-conditioning, and service openings are secured with steel bars, metal grating, or an alarm system.
(D) Any metal grates have spaces no larger than 6 inches wide measured in any direction.
(E) Any metal screens have spaces no larger than 3 inches wide measured in any direction.
(F) All steel bars shall be no further than 6 inches apart.
Apparently there is no requirment for a dealer to secure weapons in a safe or strong room of any sort.