Elections Code § 8227
ARTICLE 2. Adoption of Subdivision (d) of Section 16 of Article VI of the California Constitution
Upon the adoption of the ordinance or resolution or the presentation of a petition, the board of supervisors shall submit the proposal to the voters at the next succeeding general election, presidential primary, or countywide special election, occurring subsequent to 90 days after the adoption of the ordinance or resolution or the presentation of the petition.