CA Gov't Code Section 57330.5

(a)

If a city annexes land that is subject to a contract executed pursuant to the Williamson Act (Chapter 7 (commencing with Section 51200) of Division 1), and the city succeeds to the contract pursuant to either Section 51243 or Section 51243.5, then on and after the effective date of the annexation, the city has all of the rights, duties, and powers imposed by that contract.

(b)

If a city annexes land that is subject to a contract executed pursuant to the Williamson Act (Chapter 7 (commencing with Section 51200) of Division 1), and the city exercises its option to not succeed to the contract pursuant to Section 51243.5, then the city shall record a certificate of contract termination pursuant to that section.