California Code, Elections Code - ELEC § 9144

If a petition protesting the adoption of an ordinance is submitted to the county elections official before the effective date of the ordinance, the ordinance shall be suspended and the board of supervisors shall reconsider the ordinance. The petition shall be signed by voters of the county equal in number to at least 10 percent of the entire vote cast within the county for all candidates for Governor at the last gubernatorial election.