Cal. Gov. Code § 68097.3
Whenever a member of the California Highway Patrol is not subject to a subpoena pursuant to Section 1989 of the Code of Civil Procedure, he may nevertheless be required to appear as a witness before any court located in this state, in any civil action or proceeding in connection with a matter regarding an event or transaction which he has perceived or investigated in the course of his duties, by a subpoena requiring his attendance. The subpoena may be served by delivering a copy (1) to the member personally or to his immediate superior or (2) during usual office hours, at least five days prior to the date of the member's required attendance, to the person in charge of the office of the California Highway Patrol where the member filed his report of the event or transaction.
Ca. Gov. Code § 68097.3