California Code, Public Resources Code - PRC § 25206

The terms of office of the members of the commission shall be for five years, except that the members first appointed to the commission shall classify themselves by lot so that the term of office of one member shall expire at the end of each one of the five years following the effective date of this division.  Any vacancy shall be filled by the Governor within 30 days of the date on which a vacancy occurs for the unexpired portion of the term in which it occurs or for any new term of office.

If the Governor fails to make an appointment for any vacancy within such 30-day period, the Senate Rules Committee may make the appointment to fill the vacancy for the unexpired portion of the term in which the vacancy occurred or for any new term of office, subject to the provisions of Section 25204.