Cal. Pub. Util. Code § 12305

A district may make all or part of its officers, whether elective or appointive, or both, and employees members of the Public Employees’ Retirement System by contract entered into between the district and the board of administration of the system under the Public Employees’ Retirement Law (Part 3 (commencing with Section 20000) of Division 5 of Title 2 of the Government Code); and the district may perform all acts necessary or convenient for that participation.