The national monuments of Trump’s April executive order, meanwhile, are areas of federally owned land set aside for their natural beauty or cultural significance. They are somewhat akin to national parks, except that a president can unilaterally designate a national monument under the Antiquities Act of 1906. A national park can only be created by an act of Congress.

...can't change history, but you can learn from it. Robert E Lee, Stonewall Jackson - who's next, Washington, Jefferson? So foolish! Also... — Donald J. Trump (@realDonaldTrump) August 17, 2017

One of the sites most likely to be downsized is Bears Ears National Monument in southeastern Utah, which was created by the Obama administration in December of last year. It encompasses more than 2,000 square miles of wilderness—desert, shrub, canyon, and peak—including two enormous buttes that give the area its name.

Since the late 1990s, some Republicans, especially in the West, have argued that national monuments created by the Clinton and Obama administrations were too large and exceeded the Antiquities Act’s authority. Bears Ears came under particular attack.

“The Antiquities Act does not give the federal government unlimited power to lock up millions of acres of land and water, and it’s time that we ended this abusive practice,” said Trump as he signed the order.

He promised to “return control [of the land] to the people, the people of all of the states, the people of the United States.”

Another group of people responded very differently to the Bears Ears announcement. Five indigenous nations lobbied the U.S. government to preserve the land, saying it holds historical, cultural, and sacred significance to their people.

“[The designation of Bears Ears] actually brought tears to my face,” said Eric Descheenie, a member of the Navajo nation and an Arizona state legislator. “It’s so hard to even try to add up what this really means. At the end of the day, there’s only a certain place in this entire world, on Earth, where we as indigenous peoples belong.”

The Antiquities Act was written more than a century ago in part to prevent “pothunting,” the theft of indigenous artifacts from unprotected sites on public land. Bears Ears, which contains dozens of uninhabited Native cultural and archaeological sites, had been the target of considerable pothunting.

In 2009, federal agents raided the nearby town of Blanding, Utah, arresting 17 suspects and seizing thousands of allegedly stolen artifacts. Locals say that the raid was too broad and that it led to tragic consequences. Many also believe that pothunting is a way of life.

But the huge number of artifacts the raid recovered shocked Native nations into action. Indigenous leaders felt that some kind of lasting federal protection must be extended to the Bears Ears area, and they worked with Utah’s congressional delegation for years to try to secure protection.