25 U.S.C. § 352b

Where patents in fee have been issued for Indian allotments, during the trust period, without application by or consent of the patentees, and such patentees or Indian heirs have sold a part of the land included in the patents, or have mortgaged the lands or any part thereof and such mortgages have been satisfied, such lands remaining undisposed of and without incumbrance by the patentees, or Indian heirs, may be given a trust patent status and the Secretary of the Interior is, on application of the allottee or his or her Indian heirs, hereby authorized, in his discretion, to cancel patents in fee so far as they cover such unsold lands not encumbered by mortgage, and to cause new trust patents to be issued therefor, to the allottees or their Indian heirs, of the form and legal effect as provided by the Act of February 8, 1887 ( 24 Stat. 388 ), such patents to be effective from the date of the original trust patents, and the land shall be subject to any extensions of the trust made by Executive order on other allotments of members of the same tribe, and such lands shall have the same status as though such fee patents had never been issued: Provided , That this section and section 352a of this title shall not apply where any such lands have been sold for unpaid taxes assessed after the date of a mortgage or deed executed by the patentee or his heirs, or sold in execution of a judgment for debt incurred after date of such mortgage or deed, and the period of redemption has expired.