Cal. LAB § 1151.4

(a) Complaints, orders, and other process and papers of the board, its members, agents, or agency, may be served either personally or by registered mail or by telegraph, or by leaving a copy thereof at the principal office or place of business of the person required to be served. The verified return by the individual so serving the same setting forth the manner of such service shall be proof of the same, and the return post office receipt or telegraph receipt therefor when registered and mailed or telegraphed as provided in this subdivision shall be proof of service of the same. Witnesses summoned before the board, its members, agents, or agency, shall be paid the same fees and mileage that are paid witnesses in the courts of the state, and witnesses whose depositions are taken and the persons taking the same shall severally be entitled to the same fees as are paid for like services in the courts of the state.

(b) All process of any court to which application may be made under this part may be served in the county where the defendant or other person required to be served resides or may be found.