California Code, Streets and Highways Code - SHC § 25073

If an even number of counties comprise a district, an additional member of the board of directors shall be appointed by the directors already named in behalf of the several boards of supervisors.  If the directors fail to make the appointment within 30 days after the date set for the first meeting of the board of directors, the secretary of the board shall, or any member thereof may, notify the Director ofTransportation of that fact and he shall, within 30 days after receiving the notification, appoint a member of the board of supervisors of any county within the district, or a person residing in the district and owning real property within the boundaries thereof, to serve as the additional member of the board of directors.