Legal Question in Landlord & Tenant Law in California

Sure, a UD case can be filed whenever it is alleged a tenant in possession should be evicted. There is no difference between a long term lease and a month to month one except for the duration of the period of the rental period.

Mr. Shers is correct but I want to emphasize that there must be grounds for claiming unlawful detainer exists, i.e., the tenant no longer has a right of possession, such as for non-payment of rent or other incurable breach of the lease. Had the landlord given notice that the tenancy would terminate at the end of the lease period and the tenant stayed, that also would be an unlawful detainer. If the landlord accepted further rents after the initial lease expired, however, the occupancy converted to a tenancy at will. The landlord can still terminate that tenancy by giving sixty-days notice and accepting no rents for occupancy beyond the sixty days (it would be thirty-days if the tenants had occupied the property for less than a year). If the tenant then does not move out at the end of the sixty days, an unlawful detainer would exist at that point and eviction proceedings could be filed.