Documents obtained by The Associated Press and The Washington Post showed the administration plans to reduce the 1.3 million-acre monument by nearly 85 percent. The plans aim to shrink Grand Staircase-Escalante by almost half, according to the documents.
Former President Barack Obama designated Bears Ears last year in an effort to protect land that several Native American tribes consider sacred. Many Republicans and rural residents loathed the move, calling it federal overreach and saying it blocked energy development.
In a statement Thursday, Sen. Orrin Hatch, R-Utah, praised the expected announcement, saying that Trump was giving “the people of Utah a voice in this process.”
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"Following Secretary Zinke’s fair, thorough, and inclusive review, [this] will represent a balanced solution and a win for everyone on all sides of this issue.
During Saturday’s protest, people carried signs comparing the land to a temple and telling the president he was making "a monumental mistake."
"We need places like Bears Ears where the land remains largely untouched — where the plants remain pure [and] the minerals remain pure because that affects the potency of our prayers and the potency of our ceremonies," said one of the speakers, Navajo Nation Attorney General Ethel Branch.
Meanwhile, Trump supporters gathered at a courthouse in Monticello, Utah. One of the speakers, San Juan County Commissioner Bruce Adams, said in an interview that he wants people to be able to drive in Bears Ears — its roads were closed under the monument designation — and to ensure that it remains open for grazing and other agricultural activities.
"It's a way of life for people down there," he said.
Adams said there would be “a greater possibility” of uranium mining in the area without federal protections, though he said that he doesn’t want “big corporations” to develop it.
"We want the land to pretty much remain the way it is," he said, adding that he’s mostly frustrated with the "control and overreach of the federal government."
"We feel like we've had a big target on our back," he said. "They've tried to reduce extraction in our county where it makes sense."
The announcement will likely trigger a legal fight from conservationists and Native American groups, who have said the Trump doesn’t have the legal authority to undo Obama's designation.
Ryan Beam, of the Center for Biological Diversity, said the Antiquities Act, which established the national monument system, doesn't allow for their elimination.
Even though Trump's apparent plan would only reduce their size, Beam argued that those reductions would effectively eliminate the system's protections.
"As soon as Trump takes action, our organization ... along with many others will quickly bring them to court," he said. "And that's a legal battle that we fully expect to win."
Geoff Bennett is a White House correspondent for NBC News.
Tim Stelloh is a reporter for NBC News, based in California.
Steve Patterson is a correspondent in Los Angeles for NBC News.