In Colorado, a residential lease agreement can be no longer than one (1) year. If the tenant and landlord agree to rent for more than one year, the term must be explicitly stated in a written lease.
Verbal lease agreements are permitted, but any tenancy duration of one year or more must be in writing. It is recommended that all lease agreements be written down and signed so they can be enforced.
If there is no lease agreement or no term is specified, the tenancy is assumed to be on a month-to-month basis.
The information for this answer was found on our Colorado Residential Lease Agreement answers.