Cal. Civ. Code § 704.03

704.03 Requirement of writing for rental agreements and termination.
(1) Original agreement. Notwithstanding s. 704.02, a lease for more than a year, or a contract to make such a lease, is not enforceable unless it meets the requirements of s. 706.02 and in addition sets forth the amount of rent or other consideration, the time of commencement and expiration of the lease, and a reasonably definite description of the premises, or unless a writing, including by means of electronic mail or facsimile transmission, signed by the landlord and the tenant sets forth the amount of rent or other consideration, the duration of the lease, and a reasonably definite description of the premises and the commencement date is established by entry of the tenant into possession under the writing. Sections 704.05 and 704.07 govern as to matters within the scope of such sections and not provided for in such written lease or contract.
(2) Entry under unenforceable lease. If a tenant enters into possession under a lease for more than one year which does not meet the requirements of sub. (1), and the tenant pays rent on a periodic basis, the tenant becomes a periodic tenant. If the premises in such case are used for residential purposes and the rent is payable monthly, the tenant becomes a month-to-month tenant; but if the use is agricultural or nonresidential, the tenant becomes a year-to-year tenant without regard to the rent-payment periods. Except for duration of the tenancy and matters within the scope of ss. 704.05 and 704.07, the tenancy is governed by the terms and conditions agreed upon. Notice as provided in s. 704.19 is necessary to terminate such a periodic tenancy.
(3) Assignment. An assignment by the tenant of a leasehold interest which has an unexpired period of more than one year is not enforceable against the assignor unless the assignment is in writing reasonably identifying the lease and signed by the assignor; and any agreement to assume the obligations of the original lease which has an unexpired period of more than one year is not enforceable unless in writing signed by the assignee.
(4) Termination of written lease prior to normal expiration date. An agreement to terminate a tenancy more than one year prior to the expiration date specified in a valid written lease is not enforceable unless it is in writing signed by both parties. Any other agreement between the landlord and tenant to terminate a lease prior to its normal expiration date, or to terminate a periodic tenancy or tenancy at will without the statutory notice required by s. 704.19 may be either oral or written. Nothing herein prevents surrender by operation of law.
(5) Proof. In any case where a lease or agreement is not in writing signed by both parties but is enforceable under this section, the lease or agreement must be proved by clear and convincing evidence.