Cal. Penal Code § 1360

The clerk or judge receiving and opening the commission and return shall immediately file it, with the affidavit mentioned in Sections 1358 and 1359, in the office of the clerk of the court in which the indictment is pending. If the commission and return is transmitted by mail, the clerk to whom it is addressed shall receive it from the post office, and open and file it in his or her office, where it must remain, unless otherwise directed by the court or judge.