Colorado Revised Statutes Title 39. Taxation § 39-5-102. When schedules required--nonresident owners listed

(1) Ownership of real property shall be ascertained by the assessor from the records of the county clerk and recorder, and owners of real property shall not be required to file schedules listing the same; but any person having or claiming to have an undivided interest in any real property, or any inchoate, possessory, or equitable interest therein, or any other estate less than the fee, or any lien on any real property may file a schedule with the assessor, specifying such interest.

(2) When the ownership of any real or personal property cannot be ascertained by the assessor after due diligence, he may list such property under the legend “owner unknown”.

(3) The assessor shall furnish annually by the first day of June to the executive director of the department of revenue a list of the names and addresses of all nonresidents of the state as shown by the assessor's records as of the previous assessment date to have owned real or personal property within the county.