California Code, Government Code - GOV § 34906

Notwithstanding Section 36503, if a city has an elected mayor and the election of the remaining members of the city council for four-year terms is not evenly staggered, the city council may, on a one-time basis only and prior to the first day for circulating nomination papers for the general municipal election, designate one of the city council offices appearing on the general municipal ballot, other than the office of the mayor, to serve a two-year term, or may provide that of the city council offices appearing on the general municipal ballot, other than the office of the mayor, the one which receives the least votes of those elected (or if there is a tie for such a position, as decided by lot) shall serve a two-year term. At all subsequent general municipal elections, each member of the city council elected at such election, other than the mayor if the mayor has a two-year term, shall be elected to serve a four-year term.