Cal. Pub. Util. Code § 6465

The resettlement franchise may be amended from time to time by ordinance passed by the governing or legislative body of the city or city and county and ratified by the electors of the city or city and county in the manner prescribed for the passage of the resettlement franchise in the first instance, and not otherwise. No such amendment is effective unless accepted in writing by the grantee of the resettlement franchise.