30 U.S.C. § 86
In any Indian reservation opened to settlement and entry pursuant to a classification of the surplus lands therein as mineral and nonmineral, such surplus lands not otherwise reserved or disposed of, which have been or may be withdrawn or classified as coal lands or are valuable for coal deposits, shall be subject to the same disposition as is or may be prescribed by law for the nonmineral lands in such reservation whenever proper application shall be made with a view of obtaining title to such lands, with a reservation to the United States of the coal deposits therein and of the right to prospect for, mine, and remove the same. Such surplus lands, prior to any disposition hereunder, shall be examined, separated into classes the same as are the nonmineral lands in such reservations, and appraised, as to their value, exclusive of the coal deposits therein, under such rules and regulations as shall be prescribed by the Secretary of the Interior for that purpose.
30 U.S.C. § 86