Friendship Hill National Historic Site was created through the "National Parks and Recreation Act of 1978". The text of the relevant section is below:
Public Law 95-625 - National Parks and Recreation Act of 1978
Sec. 509. (a) The Secretary is authorized to establish the Friendship Hill National Historic Site in the State of Pennsylvania, including the former home of Albert Gallatin, as depicted on the map entitled "FRHI-80000" dated February 1978. Said map shall be on file and available for public inspection in the offices of the Director, National Park Service, Washington, District of Columbia. The Secretary is authorized to acquire such land, improvements, and any personal property of cultural and historical value thereon by donation, purchase with donated or appropriated funds, or exchange.
(b) Pending establishment of the site and thereafter the Secretary shall administer property acquired pursuant to this section in accordance with the Act of August 25,1916 (39 Stat. 535; 16 U.S.C. 1, 2-4), as amended and supplemented, and the Act of August 21, 1935 (49 Stat. 666; 16 U.S.C. 461-467), as amended.
(c) (1) There are hereby authorized to be appropriated from the Land and Water Conservation Fund, such sums as may be necessary to carry out the purposes of this section.
(2) For the development of essential facilities there are authorized to be appropriated for the fiscal year ending September 30, 1980, and for succeeding fiscal years, such sums as may be necessary to carry out the purposes of this section, but not to exceed $100,000. Within three years from the effective date of this section, the Secretary shall develop and transmit to the Committee on Interior and Insular Affairs of the House of Representatives and to the Committee on Energy and Natural Resources of the Senate a general management plan for the use and development of the site consistent with the purposes of this section, indicating—
(A) the lands and interests in lands adjacent or related to the site which are deemed necessary or desirable for the purposes of resource protection, scenic integrity, or management and administration of the area in furtherance of the purposes of this section and the estimated cost thereof;
(B) the number of visitors and types of public use within the site which can be accommodated in accordance with the protection of its resources; and
(C) the location and estimated cost of facilities deemed necessary to accommodate such visitors and uses.
