September 9, 1944: William S. Hart executes Last Will and Testament. Leaves his Newhall estate, associated personal possessions, and $150,000
to County of Los Angeles. Of the $150,000, earned interest and $10,000 of principal may be withdrawn annually for operations and maintenance of future park and museum.
June 23, 1946: Hart dies. Widow and son initiate protracted and ultimatly unsuccessful legal battle for control of estate.
August 2, 1957: Court matters being concluded, Los Angeles County Board of Supervisors formally accepts Hart's bequest.
September 20, 1959: Dedication of William S. Hart Park and Museum. Los Angeles County Museum (NHMLA predecessor) operates the museum; County Parks & Recreation
Department operates the park. Museum and park staff members are county employees. Museum staff curates collection and conducts public tours.
May 15, 1962: To settle interagency disputes, Board of Supervisors places both museum and park under control of Parks Department.
1966: Los Angeles County Museum of Natural History Foundation receives federal tax-exempt status. NHMLA workers are employees of the nonprofit foundation, not the county.
(NHMLA is not involved in Hart Museum operations at this time.)
December 2, 1981: The Friends of Hart Park and Museum (FOHP), a volunteer group of local residents, incorporates as a California nonprofit corporation. Its purpose is to assist the County of Los Angeles
in fundraising, preservation and interpretation of the museum and park. FOHP serves as custodian of Hart property and collection, and conducts museum tours. Betty Pember, daughter of early-20th-century Newhall businessman Lloyd Houghton,
is first FOHP president.
Circa 1983: FOHP begins asking NHMLA for assistance in preservation of Hart collection.
March 1, 1985: FOHP receives federal tax-exempt status.
May 1986: FOHP receives grant funds from Institute of Museum and Library Services (IMLS) for inventory and appraisal of Hart collection. Additional grant funds are received in 1987 from Aetna Insurance Co.
June 24, 1986: Motion by Supervisor Michael D. Antonovich instructs County Chief Administrative Officer (CAO), Parks and NHMLA directors to conduct study of how best to conserve,
preserve, interpret and offer a viable public program for Hart estate. Motion carries.
December 16, 1986: At FOHP's request, Antonovich seeks Board approval for $166,810 to pay for an NHMLA curator to care for the collection through fiscal year-end; and to
place the museum (mansion, ranch house, bunkhouse) under NHMLA management. NHMLA is to "confer with the Friends of Hart Park  on program development." Motion subsequently withdrawn on recommendation of CAO to defer until 1987-88 budget year.
April 1, 1987: NHMLA assigns a curatorial assistant, Katherine Child, to the Hart Museum one day per week to begin "registration" (inventory) of the collection.
1987: At FOHP request, Antonovich reintroduces motion for funding and NHMLA operational management of Hart Museum. Board of Supervisors approves.
September 1, 1987: NHMLA takes over operational management of Hart Museum. Child subsequently named curator of collection.
December 1987: NHMLA begins removal of Hart documents,
manuscripts, photographs, press clippings and scrapbooks to NHMLA's Seaver Center of Western History Research in Los Angeles for long-term care.
FOHP publicly objects, citing the will: "The museum property shall be maintained in its present location..." Certain items, such as Hart's jewelry collection,
had already been removed. NHMLA director expresses intent to place Hart items on display at other facilities in future.
January 1988: FOHP and NHMLA reach agreement. NHMLA chief deputy director Mark Rodriguez assures the materials will eventually be returned.
January 10, 1989: NHMLA policy statement outlines NHMLA's responsiblities for care of Hart collection and support services (including tours).
NHMLA is charged with "supporting and providing resources as necessary and appropriate" to FOHP and "encourag[ing] close cooperation and
mutual support in achieving the objectives of the Friends and Museum Foundation."
November 29, 1989: Self-renewing agreement between County and FOHP memorializes FOHP's duty to solicit, receive, administer and distribute funds and
otherwise assist in improving and expanding County parks and recreation services.
March 1, 1991: NHMLA reorganization shifts administration and day-to-day operation of Hart Museum from NHMLA's History Division to its Education Division.
NHMLA assigns museum admininstrator; NHMLA's separate volunteer pool conducts tours. NHMLA's Rodriguez informs FOHP that the Hart materials will be housed at Seaver Center "until a properly equipped and staffed
research library is established at the Hart Park Museum facility."
Present Day: The materials have not been returned, and no on-site research library has been established.