Cal. Rev. & Tax. Code § 11475

In any action brought under this part, process may be served according to the Code of Civil Procedure and the Civil Code or may be served upon any agent or clerk in this state employed by any private railroad car company in a place of business maintained by the private railroad car company in this state. In the latter case, a copy of the process shall be sent by registered mail to the private railroad car company at its principal or home office.