Cal. Elec. Code § 15210

In preparing the voted ballots for processing, any ballot that is torn, bent, or otherwise defective shall be corrected so that every vote cast by the voter shall be counted by the automatic tabulating equipment. If necessary, a true duplicate copy of the defective ballot shall be made and substituted therefor, following the intention of the voter insofar as it can be ascertained from the defective ballot. All duplicate ballots shall be clearly labeled “duplicate,” and shall bear a serial number that shall be recorded on the damaged or defective ballot.