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(NEXSTAR) – The National Park Service currently oversees 423 sites and is studying another 21 for possible consideration to join the system. But even if these sites do receive national park status, they could still lose it.

A more recent example of this is the Oklahoma City National Memorial. In April 1995, 168 people were killed when a bomb exploded outside the Alfred P. Murrah Federal Building in Oklahoma City. Considered the worst act of homegrown terrorism in the nation’s history, the incident would go on to be known as the Oklahoma City Bombing.

Two years later, President Bill Clinton signed an act into law creating the Oklahoma City National Memorial Trust, which was responsible for creating the Oklahoma City National Memorial as a unit of NPS. It was officially completed in 2001.

Three years later, President George W. Bush transferred the memorial to the Oklahoma City National Memorial Foundation instead and declared it an affiliate area of NPS, ultimately removing it from the more than 400 sites NPS directly oversees. The Oklahoma City National Memorial, which was able to keep its name, isn’t the first to see its NPS status change.

The first park to ever be divested was actually the second national park to ever exist in the U.S.: Mackinac National Park. The park was established in 1875 on Michigan’s Mackinac Island, which the federal government already owned thanks to Fort Mackinac. When the military left the island in 1895, the War Department – which oversaw the national park at the time – decided it was best to transfer the park to the state of Michigan, according to a report on Mackinac’s history and significance.

The park is now known as Mackinac Island State Park and covers more than 80% of the island.

During the 1900s, multiple national monuments enacted by sitting presidents were abolished. Under the Antiquities Act, the president has the power to create national monuments. All other national park sites must be created by an act of Congress (which can also create national monuments). Congress is also responsible for divesting NPS sites.

Various reasons for the abolishment of the national monuments are listed in a survey from 1983 the NPS shared with Nexstar: two were declared extraneous and transferred to their respective states; two were difficult to develop and reach or access and were transferred to the U.S. Forest Service; resources were declared depleted in one; another was handed off to its state because it was “historically inaccurate.” Five others were simply transferred to their state or another agency for better management.

One of the monuments labeled “extraneous,” Father Millett Cross in New York, can still be visited today. After being turned over to the state in 1949, Father Millett Cross became part of what is now Fort Niagra State Park in Youngstown. The other extraneous monument, Castle Pinckney, was abolished in 1956 after never receiving visitors. After changing hands several times, Castle Pinckney, located on the southern tip of Shutes Folly Island off the coast of Charleston, South Carolina, was purchased by the Sons of Confederate Veterans in 2011.

Other sites have simply been hard to reach, like Mount of the Holy Cross found among Colorado’s mountains and Alaska’s Misty Fjords (now Misty Fjords National Monument Wilderness within Tongass National Forest).

Perhaps one of the most interesting abolished monuments was Verendrye in Pierre, South Dakota. Designated by President Woodrow Wilson in 1917, the site was said to be where the sons of French explorer Sieur de Verendrye camped during their explorations in 1742. Historians later determined the site was inaccurate and Verendrye National Monument was abolished in 1956.

FILE – Donald Trump’s Mar-a-Lago resort in Palm Beach, Fla., is seen Friday, Aug. 30, 2019. (AP Photo/Lynne Sladky, File)

Before being purchased by President Donald Trump in the 1980s, Mar-a-Lago was actually part of NPS. After being designated as a national historic site, the Florida estate was placed under NPS’s authorization in 1972. Due to “maintenance and security concerns,” the federal government returned Mar-a-Lago to the Post Foundation (Marjorie Merriweather Post owned the home before her death), which later sold the property to Trump.

Another, Fossil Cycad National Monument in the Black Hills of South Dakota, was established by President Warren G. Harding in 1922 after hundreds of fossils and fossilized specimens were exposed. But, because of “years of negligent management” and fossils disappearing (either naturally or by people to research and display) faster than erosion could expose more, Fossil Cycad was considered to be depleted. In 1957, Congress voted to reauthorize the site, which is now managed by the Bureau of Land Management.

Most abolished sites follow the same trajectory as the Oklahoma City National Memorial or Mackinac National Park – they become the responsibility of the state or another group dedicated to maintaining them.