California Code, Government Code - GOV § 51255

(a) Notwithstanding any other provision of this chapter, the parties may upon their mutual agreement rescind a contract in order simultaneously to enter into an open-space easement agreement pursuant to the Open-Space Easement Act of 1974 (Chapter 6.6 (commencing with Section 51070)), provided that the easement is consistent with the Williamson Act (this chapter) for the duration of the original Williamson Act contract.  The easement would enforceably restrict the same property for an initial term of not less than 10 years and would not be subject to the provisions of Article 4 (commencing with Section 51090) of Chapter 6.6.  This action may be taken notwithstanding the prior serving of a notice of nonrenewal, and the land subject to the contract shall be assessed pursuant to Section 423 of the Revenue and Taxation Code.

(b) This section shall not apply to any agreement entered into on or before August 12, 1998.