C.R.S. § 36-1-126: Delinquent payments.

When any purchaser of land defaults for a period of thirty days in any of the payments of either principal or interest due upon the certificate of purchase issued to him, the certificate may be forfeited and the lands reverted to the state upon a notice to that effect mailed to the last-known post-office address of the purchaser, which notice shall allow him thirty days additional in which to pay the indebtedness to the state.