California Code, Elections Code - ELEC § 17602

(a) The following provisions shall apply to all state or local elections not provided for in subdivision (a) of Section 17601. An election is not deemed a state or local election if votes for candidates for federal office may be cast on the same ballot as votes for candidates for state or local office.

(b) The following data shall be kept by the elections official, on electronic media, stored and unaltered, for six months from the date of the election:

(c) If a contest is not commenced within the six-month period, or if a criminal prosecution involving fraudulent use, using the ballot tally system to mark or falsify ballots, or manipulation of the ballot tally system is not commenced within the six-month period, either of which may involve the vote count of the precinct from which voted ballots were received, the elections official shall have the backups destroyed.