The Secretaries of the Departments of Interior and Agriculture, for the purpose of eliminating private holdings within the Yosemite National Park and to preserve intact timber along and adjoining the roads in the scenic portion of the park on patented lands, are empowered in their discretion to obtain and accept for the United States a complete title to any and all patented lands within the boundaries of said park by the exchange of timber or timber and lands within the Yosemite National Park and the Sierra and Stanislaus National Forests for such lands and the timber thereon within the park, necessary conveyances of park and national forest timber or timber and lands to be made by said secretaries, respectively. The secretaries of the said departments are authorized to acquire title in fee by the exchange of lands of the United States for patented lands not exceeding six hundred and forty acres in the Sierra and Stanislaus National Forests, adjacent and contiguous to the Yosemite National Park, and when such patented lands are thus acquired, said lands shall become a part of the Yosemite National Park and be subject to all the provisions of sections 55, 61, 471c and 471d of this title.