California Code, Public Utilities Code - PUC § 15960

The board of supervisors shall number, name, and designate each territorial unit of the district by ordinance at a regular or special meeting after the formation of the district, and in time to permit publication and taking effect of the ordinance before the earliest time when nominating certificates and declarations of candidacy for the board of directors may be filed. The ordinance shall remain in force until the board of directors of the district, by ordinance, shall number, name, and designate the territorial units.