“The question has never been whether to protect them, but how to protect them best,” said Gov. Spencer Cox, a Republican. His office assured the lands left out of the modified boundaries “remain protected under existing federal and state law.”

But some conservationists and citizens of local tribal nations warned the order opens the door to mining while disrespecting tribal co-stewardship. Bears Ears is jointly managed by an agreement between tribal nations and federal agencies.

“Our connection to this place cannot be erased by the stroke of a pen,” said Davina Smith-Idjesa, a citizen of the Navajo Nation and co-chair of the Bears Ears Inter-Tribal Coalition.

Is it legal to shrink or eliminate monuments?

Environmental groups have argued the Antiquities Act is a one-way road that allows presidents to create but not undo monuments. But there’s a history of presidents taking actions similar to Trump’s.

Since 1912, presidents have issued more than a dozen proclamations that diminished monuments, according to a National Park Service database.

In Washington state, Woodrow Wilson reduced the acreage of Mount Olympus National Park — now Olympic National Park — by roughly half. Harry Truman did the same for Santa Rosa Island National Monument.

Dwight Eisenhower was most active in undoing proclamations of his predecessors as he diminished six monuments, including Arches in Utah, Great Sand Dunes in Colorado and Glacier Bay in Alaska, which have all since become national parks.

How is a national monument different from a national park or forest?

Unlike national parks, which are established by Congress, most of the more than 100 national monuments were created by presidents.

They’re governed by one or more agencies such as the National Park Service, Bureau of Land Management or National Oceanic and Atmospheric Administration.

A designation provides sweeping protections not just for significant geological features or artifacts but also for the surrounding landscape, banning drilling, mining and new construction.

The U.S. Forest Service was established in 1905 and has jurisdiction over some 300,000 square miles (775,000 square kilometers) of land, including 154 national forests and 20 national grasslands in 43 states.

Under federal law, the forest lands are managed for renewable resources — including timber, clean water, wildlife habitat, forage for livestock and recreation. Many forests overlay valuable minerals, and parcels can be leased by private companies for the extraction of nonrenewable resources such as oil, gas and coal.

National parks have some of the most stringent rules against development under a 1916 law known as the Organic Act. The law says the fundamental purpose of the parks is to conserve their scenery, nature, history and wildlife.

How long have presidents been creating monuments?

President Theodore Roosevelt signed the Antiquities Act after a generation of lobbying by educators and scientists who wanted to protect sites from commercial artifact looting and haphazard collecting by individuals. It was the first law in the U.S. to establish legal protections for cultural and natural resources of historic or scientific interest on federal lands.

On Sept. 24, 1906, Roosevelt used it to designate a national monument at Devils Tower — a giant rock butte in eastern Wyoming that later gained fame as the focus of the movie “Close Encounters of the Third Kind.”

All but three presidents have used the act to protect unique landscapes and cultural resources.

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Brown reported from Billings, Mont.

Matthew Brown And Hannah Schoenbaum, The Associated Press