California Code, Government Code - GOV § 23720

(a) A county charter may be amended by proposals submitted by the governing body or by a petition signed by 10 percent of the qualified electors of the county, computed upon the total number of votes cast in the county for all candidates for Governor at the last general election at which a Governor was elected, filed in the office of the county elections official, petitioning the governing body to submit a proposed amendment or amendments to the charter of the county to the qualified electors of the county, which amendment or amendments are set forth in full in the petition.

(b) A county charter may be repealed by proposals submitted by the governing body or by a petition signed by 10 percent of the qualified electors of the county computed upon the total number of votes cast in the county for all candidates for Governor at the last general election at which a Governor was elected.  The petition, petitioning the governing body to submit the question of charter repeal to the qualified electors of the county, shall be filed in the office of the county elections official.

(c) Petitions to amend or repeal a county charter shall be subject to Article 1 (commencing with Section 9100) of Chapter 2 of Division 9 of the Elections Code.