California Code, Harbors and Navigation Code - HNC § 6055

The commissioners elected at the first election shall, within 10 days from the date of the canvass of the returns of the election, enter upon the duties of office. Before entering upon the duties of his or her office, each commissioner shall take and subscribe the official oath before the secretary or an officer authorized by law to administer oaths and shall file it with the county elections official of the county in which the district is situated.

They shall elect one of their number as president or chairperson and one of their number as secretary. The president or chairperson and secretary shall serve at the pleasure of the board.