Cal. Com. Code § 10600

This division shall apply to all lease contracts that are first made or that first become effective between the parties on or after January 1, 1990. This division shall not apply to any lease contract first made or that first became effective between the parties prior to January 1, 1990, or to any extension, amendment, modification, renewal, or supplement of or to the lease contract, unless the parties thereto specifically agree in writing that the lease contract, as extended, amended, modified, renewed, or supplemented, shall be governed by this division.