On December 3, 2004, President George W. Bush signed the Petrified Forest Expansion Act into law, more than doubling the authorized acreage of the park. The Act provided the authority for the National Park Service to acquire approximately 125,000 acres of private and State lands from willing sellers and the transfer of Bureau of Land Management (BLM) lands within the new boundary to the NPS.
On May 18, 2007, the BLM transferred administrative jurisdiction of approximately 15,228 acres of public lands to the National Park Service.
The funds for acquisition of lands come through the Land and Water Conservation Fund (LWCF), a federal land protection program that receives significant revenue from the development of federally-owned offshore oil and gas rights. No taxpayer dollars are used to support the fund, which has been protecting forests, natural resources, state and local parks and recreation areas since 1965. Petrified Forest National Park must compete for LWCF funds with other worthy projects across the National Park Service.
On September 8, 2011, with the help of The Conservation Fund , the former Paulsell Ranch was purchased from the Hatch family, adding 25,876 acres primarily to the eastern portion of the park.
In January of 2013, The Conservation Fund, in partnership with the National Parks Conservation Association, purchased the 4265 acre McCauley Ranch on the park's behalf. On December 26, 2013, the National Park Service purchased the ranch from The Conservation Fund.
On August 30, 2016, a 7629 acre portion of the NZ Milky Ranch in the southeastern portion of the park expansion was purchased by the National Park Service.
The newly acquired lands, particularly in the eastern expansion area, are in checkerboard pattern with Arizona State Trust Lands, administered by the Arizona State Land Department. Petrified Forest National Park has acquired the grazing leases on 25,052 acres of these lands and is seeking a special land use permit from the Arizona State Land Department to permit guided public access across these Trust lands.
In all the purchases from private sellers described here, mineral rights were not available for purchase and remain in private ownership. Potash, a mineral used for agricultural fertilizer, is known to exist 800 to 1400 feet below the surface of most of these lands. Should global prices for potash rise again, mining pressures on these lands, which were present from about 2008 to 2015, would likely resume.
Including several smaller parcels not highlighted above, the park has acquired over 53,000 (42% of the newly authorized lands) acres since 2007, mostly in the eastern expansion area, and is leasing another 25,000 acres (20% of the newly authorized lands) from the State of Arizona. Staff have been mapping roads and water sources, removing unneeded fences, and intensively surveying archeological and paleontological sites on the federal lands. Within the next year or so, depending upon the discussions with the Arizona State Land Department, guided public access onto these lands could be available, primarily through the park’s non-profit partner, the Petrified Forest Field Institute.