Cal. Civil Code § 3308

The parties to any lease of real or personal property may agree therein that if the lease shall be terminated by the lessor by reason of any breach thereof by the lessee, the lessor shall thereupon be entitled to recover from the lessee the worth at the time of the termination, of the excess, if any, of the amount of rent and charges equivalent to rent reserved in the lease for the balance of the stated term or any shorter period of time over the then reasonable rental value of the property for the same period. The rights of the lessor under the agreement shall be cumulative to all other rights or remedies now or hereafter given to the lessor by law or by the terms of the lease; provided, however, that the election of the lessor to exercise the remedy hereinabove permitted shall be binding upon him or her and exclude recourse thereafter to any other remedy for rental or charges equivalent to rental or damages for breach of the covenant to pay the rent or charges accruing subsequent to the time of the termination. The parties to the lease may further agree therein that unless the remedy provided by this section is exercised by the lessor within a specified time the right thereto shall be barred. This section does not apply to a lease of real property unless (a) the lease was executed before July 1, 1971, or (b) the terms of the lease were fixed by a lease, option, or other agreement executed before July 1, 1971. This section does not apply to leases subject to Division 10 (commencing with Section 10101) of the Commercial Code.