The Secretary of the Interior shall acquire on behalf of the United States by gift, purchase, condemnation, or otherwise, such lands and interest in land, together with any improvements thereon, as the Secretary may deem necessary for the purpose of establishing a national historic site commemorating the completion of the first transcontinental railroad across the United States on the site described on a map entitled “Proposed Golden Spike National Historic Site, Utah”, prepared by the National Park Service, Southwest Region, dated February 1963. In exercising his authority to acquire property by exchange, the Secretary may accept title to any non-Federal property within the area depicted on such drawing, and in exchange therefor he may convey to the grantor of such property any federally owned property in the State of Utah under his jurisdiction which he classifies as suitable for exchange or other disposal. The properties so exchanged shall be of approximately equal value, but the Secretary may accept cash from, or pay cash to, the grantor in order to equalize the values of the properties exchanged.