California Code, Health and Safety Code - HSC § 12087

No person shall abandon or otherwise dispose of any explosives in any manner which might, as the result of such abandonment or disposal, create any danger or threat of danger to life or property. Any person in possession or control of explosives required in the performance of his duties shall, when the need for such explosives no longer exists, either return the explosives to the source from which the explosives were obtained, or to an appropriate issuing authority for disposal or shall destroy the explosives in a safe manner so as not to make them available to persons who might obtain them and use them in a manner prejudicial to the safety of life and property. Magazines or temporary magazines used for storage purposes in any area where blasting is required shall, when the need for such storage no longer exists and the explosives have been removed or disposed of as above required, be removed or demolished, or signs, indicating the presence of explosives in such magazines or on the premises on which such magazines are located, shall be removed or effectively obliterated, and the issuing authority who issued the storage permit shall be immediately notified of the action taken.