The provisions of section 607 of this title, limiting the use of timber taken from public lands to residents of the State in which such timber is found, for use within said State, shall not apply to the south slope of Pryor Mountains, in the State of Montana, lying south of the Crow Reservation, west of the Big Horn River, and east of Sage Creek; but within the above-described boundaries the provisions of said section shall apply equally to the residents of the States of Wyoming and Montana, and to the use of timber taken from the above-described tract in either of the above-named States.