California Code, Public Utilities Code - PUC § 11865

(a) The remaining board members may fill the vacancy by appointment until the next district general election that is scheduled 90 or more days after the effective date of the vacancy. The appointment shall be made within a period of 60 days immediately subsequent to the effective date of such vacancy. A notice of such vacancy shall be posted in three or more conspicuous places in the district at least 15 days before the appointment is made.

In lieu of making an appointment, the remaining members of the board may within 60 days of the vacancy call a special election to fill the vacancy. The person elected at such special election shall hold office for the remainder of the term in which the vacancy occurred.

(b) If the vacancy is not filled by appointment as provided in subdivision (a), or if the board has not called for an election within 60 days of the vacancy, the board of supervisors of the county representing the larger portion of the district area in which the election to fill the vacancy will be held may fill the vacancy by appointment within 90 days of the effective date of the vacancy or may order the district to call a special election to fill the vacancy.

(c) If within 90 days of the effective date of the vacancy, the remaining members of the board or the appropriate board of supervisors have not filled the vacancy by appointment and no election has been called for, the district shall call a special election to fill the vacancy.

(d) A person elected at an election to fill a position to which an appointment was made pursuant to this section shall take office immediately upon issuance of the certificate of election by the secretary of the district, after qualifying according to law, and shall hold office for the remainder of the term in which the vacancy occurs.