If any land owned by any county is desired by the United States for national forest purposes, the board of county commissioners of such county may determine and appraise its value and may submit a copy of the appraisal to the proper agency or officer of the United States. If the willingness of the United States to pay such appraised value is expressed by appropriate action of the authorized agency or officer, the said lands may be advertised for sale in the manner provided in title 57. If no acceptable and satisfactory bid in excess of the appraised value is received, the board may sell the lands to the United States upon payment of the appraised and agreed value thereof.