California Code, Elections Code - ELEC § 14299

(a) If a precinct board is unable to furnish a ballot to a qualified voter because there is an insufficient number of ballots at the precinct, the elections official shall deliver to the precinct additional ballots to ensure that all eligible voters can cast their ballots within two hours.

(b) While awaiting the delivery of additional ballots, the precinct board shall provide each voter with the option of casting his or her vote immediately using an alternative procedure established prior to the election or waiting for the delivery of the additional ballots.

(c) The alternative procedure required by this section shall be subject to approval by the Secretary of State.  The elections official shall submit the alternative procedure to the Secretary of State for approval by a date to be determined by the Secretary of State.