Cal. Sts. & High. Code § 27043

The petition circulated in each county may consist of any number of separate copies of the original instrument and shall be signed by voters residing within the boundaries of the county or portion of the county proposed to be included in the district equal in number to at least 10 per cent of the number of voters in the county or portion thereof from which the petition is presented who voted for Governor of this State at the last general election at which a Governor was elected prior to the presentation of the petition.