Cal. PEN § 908.2

(a) Upon the decision of the superior court pursuant to Section 901 to adopt this method of selecting grand jurors, when the required number of persons have been impaneled as the grand jury pursuant to law, the jury commissioner shall write the names of each person on separate ballots. The jury commissioner shall fold the ballots so that the names cannot be seen, place them in a box, and draw out half of the ballots, or in a county where the number of grand jurors is uneven, one more than half. The persons whose names are on the ballots so drawn shall serve for 12 months until July 1 of the following year. The persons whose names are not on the ballots so drawn shall serve for six months until January 1 of the following year.

(b) Each subsequent year, on January 2 and July 2, a sufficient number of grand jurors shall be impaneled to replace those whose service concluded the previous day. Those persons impaneled on January 2 shall serve until January 1 of the following year. Those persons impaneled on July 2 shall serve until July 1 of the following year. A person may not serve on the grand jury for more than one year.

(c) The provisions of subdivisions (a) and (b) do not apply to the selection of grand jurors for an additional grand jury authorized pursuant to Section 904.6.