California Elections Code
(a) “Small city” means a city with a population of 100,000 or less, as determined by the annual city total population rankings by the Demographic Research Unit of the Department of Finance.
(b) “Eligible entity” means a school district or a special district.
(c) Notwithstanding Sections 1500 and 4000, an election in a small city or an eligible entity may be conducted wholly as an all-mail ballot election, subject to the following conditions:
(1) The legislative body of the small city or the governing body of the eligible entity, by resolution, authorizes the use of mailed ballots for the election.
(2) The election is a special election to fill a vacancy in the legislative body or governing body.
(3) The election is not held on the same date as a statewide primary or general election.
(4) The election is not consolidated with any other election.
(5) The return of voted mail ballots is subject to Section 3017.