California Code, Government Code - GOV § 23321

(a) Where the population of the proposed county is less than 5 percent of the total population of the affected counties, a petition initiating proceedings shall be signed by qualified electors residing within the territory of the proposed county as described in the petition equaling in number not less than 25 percent of the number of electors of the territory of the proposed county registered within the territory on the date of the last preceding gubernatorial election and by not less than 10 percent of the electors registered within the balance of the affected counties on the date of the last preceding gubernatorial election.

(b) Where the population of the proposed county is 5 percent or more of the total population of the affected counties, a petition initiating proceedings shall be signed by qualified electors residing within the territory of the proposed county as described in the petition equaling in number not less than 25 percent of the number of electors of the territory of the proposed county registered within the territory on the date of the last preceding gubernatorial election.

Each elector, after signing a petition, shall add the name of the county in which the elector resides, the elector's place of residence, giving a street and number or a designation sufficient to enable the place of residence to be readily ascertained, and the date the elector signed the petition.