California Code, Government Code - GOV § 57125

(a) Special elections called within all or any part of a city or registered-voter district shall be governed by the general election provisions and the local election provisions of the Elections Code, so far as they may be applicable, relating to the qualifications of voters, the manner of voting, the form of the ballot, the duties of precinct and election officers, the canvassing of returns, and all other particulars. If the commission determines that there is any inconsistency:

(b) Notwithstanding any other provision of law, special elections pursuant to this division may be conducted wholly by mailed ballot on any date other than an established election date authorized by the elections official of the county or counties affected by the use of mailed ballots.