California Code, Code of Civil Procedure - CCP § 196

(a) The jury commissioner or the court shall inquire as to the qualifications of persons on the master list or source list who are or may be summoned for jury service. The commissioner or the court may require any person to answer, under oath, orally or in written form, all questions as may be addressed to that person, regarding the person's qualifications and ability to serve as a prospective trial juror. The commissioner and his or her assistants shall have power to administer oaths and shall be allowed actual traveling expenses incurred in the performance of their duties.

(b) Response to the jury commissioner or the court concerning an inquiry or summons may be made by any person having knowledge that the prospective juror is unable to respond to such inquiry or summons.

(c) Any person who fails to respond to jury commissioner or court inquiry as instructed, may be summoned to appear before the jury commissioner or the court to answer the inquiry, or may be deemed to be qualified for jury service in the absence of a response to the inquiry. Any information thus acquired by the court or jury commissioner shall be noted in jury commissioner or court records.