California Code, Penal Code - PEN § 908

If the required number of the persons summoned as grand jurors are present and not excused, the required number shall constitute the grand jury.  If more than the required number of persons are present, the jury commissioner shall write their names on separate ballots, which the jury commissioner shall fold so that the names cannot be seen, place them in a box, and draw out the required number of them.  The persons whose names are on the ballots so drawn shall constitute the grand jury.  If less than the required number of persons are present, the panel may be filled as provided in Section 211 of the Code of Civil Procedure.  If more of the persons summoned to complete a grand jury attend than are required, the requisite number shall be obtained by writing the names of those summoned and not excused on ballots, depositing them in a box, and drawing as provided above.