C.R.S. Section 13-40-107
Notice to quit

A tenancy may be terminated by notice in writing, served not less than the respective period fixed before the end of the applicable tenancy, as follows:

(a)

A tenancy for one year or longer, ninety-one days;

(b)

A tenancy of six months or longer but less than a year, twenty-eight days;

(c)

A tenancy of one month or longer but less than six months, twenty-one days;

(d)

A tenancy of one week or longer but less than one month, or a tenancy at will, three days;

(e)

A tenancy for less than one week, one day.

(2)

Such notice shall describe the property and the particular time when the tenancy will terminate and shall be signed by the landlord or tenant, the party giving such notice or his agent or attorney.

(3)

Any person in possession of real property with the assent of the owner is presumed to be a tenant at will until the contrary is shown.

(4)

No notice to quit shall be necessary from or to a tenant whose term is, by agreement, to end at a time certain.

(5)

Except as otherwise provided in section 38-33-112, C.R.S., the provisions of subsections (1) and (4) of this section shall not apply to the termination of a residential tenancy during the ninety-day period provided for in said section.