Cal. ELEC § 12313

(a) If any member of a precinct board does not appear at the opening of the polls on the morning of an election, those voters present, including members of the board, shall appoint a voter to fill the vacancy. If none of the members appointed appears at that time, the voters of the precinct present at that time may appoint a board. (b) This section does not apply to elections conducted using vote centers.