Cal. Civ. Proc. Code § 1985.5

If a subpena requires the attendance of a witness before an officer or commissioner out of court, it shall, for a refusal to be sworn, or to answer as a witness, or to subscribe an affidavit or deposition when required, also require the witness to attend a session of the court issuing the subpena at a time and place thereof to be fixed by said officer or commissioner.