Cal. Gov. Code § 56753.5

Within 10 days after receiving a proposal that would result in the annexation to a city of land that is subject to a contract executed pursuant to the Williamson Act (Chapter 7 (commencing with Section 51200) of Division 1), the executive officer shall notify the Director of Conservation of the proposal. The notice shall include the contract number, the date of the contract’s execution, and a copy of any protest that the city had filed pursuant to Section 51243.5.