President Donald Trump has signed a proclamation to scale back two sprawling national monuments in Utah, pledging to "reverse federal overreach and restore the rights of this land to your citizens".
Mr Trump made his plans official during a speech at the state Capitol, where he was cheered by the state's Republican leaders who lobbied him to undo protections they contend are overly broad and close off the area to energy development and other access.
Environmental and tribal groups plan to sue to preserve monuments they say are vital to protect important archaeological and cultural resources, especially the Bears Ears National Monument, a more than 1.3 million-acre (2,030-square-mile) site in south-eastern Utah that features thousands of Native American artefacts, including ancient cliff dwellings and petroglyphs.
"Some people think that the natural resources of Utah should be controlled by a small handful of very distant bureaucrats located in Washington," Mr Trump said. "And guess what? They're wrong."
Around 3,000 demonstrators lined up near the State Capitol protesting his announcement. They held signs that said, "Keep your tiny hands off our public lands," and they chanted, "Lock him up!"
A smaller group gathered in support of Mr Trump's decision, including some who said they favour potential drilling or mining there that could create jobs.
The Bears Ears and Grand Staircase-Escalante national monuments were among a group of 27 monuments that Mr Trump ordered Interior Secretary Ryan Zinke to review this year.
Bears Ears, created last year by President Barack Obama, will be reduced to 201,876 acres (315 square miles).
Grand Staircase-Escalante National Monument, designated in 1996, will be reduced from nearly 1.9 million acres (nearly 3,000 square miles) to 1,003,863 acres (1,569 square miles).
Mr Trump also met with leaders of The Church of Jesus Christ of Latter-day Saints and toured Welfare Square, a church-run complex in Salt Lake City that aids the poor.
Mr Zinke accompanied the president aboard Air Force One, as did Utah's Republican senators, Orrin Hatch and Mike Lee. Mr Hatch and other Utah Republican leaders pushed Trump to launch the review, saying the monuments declared by Presidents Barack Obama and Bill Clinton locked up too much federal land.
Mr Zinke has also recommended that Nevada's Gold Butte and Oregon's Cascade-Siskiyou monuments be reduced in size, though details remain unclear. The former Montana congressman's plan would allow logging at a newly designated monument in Maine and more grazing, hunting and fishing at two sites in New Mexico.
Democrats and environmentalists have opposed the changes, accusing Mr Trump and Mr Zinke of engaging in a secretive process aimed at helping industry groups that have donated to Republican political campaigns.