Cal. Elec. Code § 13006
A user, vendor, or manufacturer shall not warehouse for a subsequent election ballot paper or ballot cards furnished or released by the Secretary of State for a specific election without first obtaining authorization in writing from the Secretary of State for the storage. The authorization shall include the particular details of the amount to be stored so that audit controls may be established and maintained. Ballot paper or ballot cards not used in that election, not authorized to be retained for subsequent elections, and not returned to the Secretary of State, shall be destroyed. A certificate of destruction setting forth the date of destruction and the amount of the ballot paper or ballot cards destroyed shall be transmitted to the Secretary of State.
Ca. Elec. Code § 13006