The maximum duration for a standard residential lease in California is one (1) year. Leases can exist for a period of greater than one year, but they need to be in writing. Oral leases are valid for shorter durations.
However, it is recommended that all leases be in written form regardless of duration. Oral leases are difficult to enforce, whereas written leases include all details agreed upon by the landlord and tenant.
If there is no duration specified on the lease, it is presumed to be a month-to-month tenancy (CA Civ Code § 1944 (2019)).
The information for this answer was found on our California Residential Lease Agreement answers.