California Code, Government Code - GOV § 23205

(a) A proposal to change the boundary line of two counties may be initiated by petition which shall contain all the matters required to be contained in a resolution adopted pursuant to Section 23203. The petition shall also designate a chief petitioner.

(b) A petition shall be signed by not less than 25 percent of the resident-voters within the affected territory or by not less than 25 percent of the property owners within the affected territory who also own not less than 25 percent of the assessed value of land and improvements within the affected territory.

(c) A petition may consist of a single instrument or separate counterparts. Each signer of a petition shall add the date of signing to his or her signature. A signature by a resident-voter shall be accompanied by the address of the voter. A signature by a property owner shall be accompanied by a description sufficient to identify the property owned.

(d) A petition shall be filed with the board of supervisors of any affected county. No petition shall be accepted for filing unless the signatures have been secured within 90 days of the date on which the first signature was affixed.

(e) Within 30 days of the receipt of a petition, the clerk of the board of supervisors shall determine whether the petition is signed by the required number of signatures. If the petition does not contain the required number of signatures, the clerk of the board of supervisors shall return the petition to the chief petitioner. If the petition contains the required number of signatures, the board of supervisors shall conduct proceedings pursuant to this article.