C.R.S. § 39-11-101: Notice to delinquent owner.

The treasurer shall make a list of all property the tax liens on which are subject to tax lien sale, describing such property as the same is described on the tax roll. Except as otherwise provided in section 39-2-117 (1)(a), no later than September 1 of each year, the treasurer shall send a notice by first-class mail, to the person's last-known mailing address, to each person by whom taxes for the previous year are known to be due and unpaid. The notice must indicate the amount of the person's delinquency and state that if the amount of the delinquency is not paid by the date specified in the notice, which shall not be less than fifteen calendar days from the date of mailing of the notice, the treasurer will advertise and sell a tax lien on the person's property on the date specified in the notice at tax lien sale for the delinquent taxes, interest, and applicable fees. If such list is not made until after September 1, the tax lien sale held thereunder shall not be void by reason thereof.