CA Penal Code § 1334.3 (2021)
2021 California Code|Penal Code - PEN|PART 2 - OF CRIMINAL PROCEDURE|TITLE 10 - MISCELLANEOUS PROCEEDINGS|CHAPTER 3a - Attendance of Witnesses Outside the State|Section 1334.3.

1334.3.  (a) If a person in any state, which by its laws has made provision for commanding persons within its borders to attend and testify in criminal prosecutions or grand jury investigations in this state, is a material witness in a prosecution pending in a court of record in this state, or in a grand jury investigation, a judge of such court may issue a certificate under the seal of the court stating these facts and specifying the number of days the witness will be required. This certificate shall be presented to a judge of a court of record in the county of such other state in which the witness is found.If the certificate recommends that the witness be taken into immediate custody and delivered to an officer of this state to assure his or her attendance in this state, the judge may direct that the witness be forthwith brought before him or her. If the judge is satisfied of the desirability of the custody and delivery, for which determination the certificate shall be prima facie proof, he or she may order that the witness be forthwith taken into custody and delivered to an officer of this state. This order shall be sufficient authority to the officer to take the witness into custody and hold him or her unless and until he or she may be released by bail, recognizance, or order of the judge issuing the certificate.If the witness is subpoenaed to attend and testify in this state, he or she shall be tendered the sum of ten cents ($0.10) for each mile necessarily traveled if the witness elects surface travel or the minimum round trip scheduled airlines fare plus twenty cents ($0.20) a mile for necessary surface travel at either end of the flight if the witness elects air travel, and except as provided in subdivision (b), a per diem of twenty dollars ($20) for each day that he or she is required to travel and attend as a witness. The judge of the court in which the witness is ordered to appear shall order the payment of witness fees authorized by law for each day the witness is required to attend the court plus reimbursement for any additional expenses of the witness which the judge of the court shall find reasonable and necessary. A witness who has appeared in accordance with the provisions of the subpoena shall not be required to remain within this state a longer period of time than the period mentioned in the certificate, unless otherwise ordered by the court. If the witness fails without good cause to attend and testify as directed in the subpoena, he or she shall be punished in the manner provided for the punishment of any witness who disobeys a subpoena issued from a court of record in this state.(b) If the witness subpoenaed to attend and testify in this state is at the time he or she is required to appear and testify an inmate of a state prison, county jail, or other penal facility, the witness shall, while attending in this state as a witness, be furnished food and lodging in the jail or other appropriate penal facility in the county in which the witness is attending court, and food and lodging of that penal facility shall be rendered in lieu of the per diem specified in subdivision (a).(Amended by Stats. 1987, Ch. 322, Sec. 3.)