Any vacancy in the membership of the commission shall be filled by appointment for the unexpired term by the board of supervisors from among the bona fide resident freeholders within the district who shall have been resident freeholders for at least one year prior to their appointment. No member of the board of supervisors, except the chairman thereof, shall be eligible to hold office on the commission or to hold any position in connection therewith.
Ca. Sts. and High. Code § 26081