The state board of land commissioners is authorized, empowered and directed to judiciously ascertain and locate the general grants of land made by congress to the state of Idaho and when said board shall find that sections 16 and 36, or any part or parts thereof, in every township of the state were sold or otherwise disposed of by or under the authority of any act of congress prior to July 3, 1890, on the admission of the state of Idaho into the union, then the said board shall by and with the approval of the secretary of the interior or the secretary of agriculture, when necessary, select from the surveyed, unreserved and unappropriated lands of the United States within the limits of the state of Idaho, other lands equivalent thereto in area and value, in legal subdivisions of not less than one-quarter (1/4) section.