The Secretary of the Interior is authorized, in his discretion, to appraise, and sell, at public auction, to the highest bidder, from time to time, under such terms as to time of payment as he may require, but in no event for any longer period than five years, any or all of the unplatted portions of Government town sites created under the Act of April 16, 1906 (34 Stat. 116), on any irrigation project constructed under the Act of June 17, 1902 (32 Stat. 388), or Acts amendatory thereof or supplementary thereto: Provided, That any land so offered for sale and not disposed of may afterwards be sold, at not less than the appraised value, at private sale, under such regulations as the Secretary of the Interior may prescribe. Patents made in pursuance of such sale shall convey all the right, title, and interest of the United States in or to the land so sold.