SALT LAKE CITY — President Trump on Monday drastically scaled back two national monuments established in Utah by his Democratic predecessors, the largest reduction of public lands protection in US history.
Trump’s move to shrink the Bears Ears and Grand Staircase-Escalante national monuments by more than 1.1 million acres and more than 800,000 acres, respectively, sparked an outpouring of praise from conservative lawmakers as well as activists’ protests outside the White House and in Utah.
It also plunges the Trump administration into uncharted legal territory since no president has sought to modify monuments established under the 1906 Antiquities Act in more than half a century.
His decision removes about 85 percent of the designation of Bears Ears and nearly 46 percent of that for Grand Staircase-Escalante, land that could now be leased for energy exploration or opened for specific activities such as motorized vehicle use.
Trump told a rally in Salt Lake City that he came to ‘‘reverse federal overreach’’ and took dramatic action ‘‘because some people think that the natural resources of Utah should be controlled by a small handful of very distant bureaucrats located in Washington. And guess what? They’re wrong.
‘‘They don’t know your land, and truly, they don’t care for your land like you do,’’ he added. ‘‘But from now on, that won’t matter.’’
Conservatives have long sought to curb a president’s unilateral power to safeguard federal lands and waters under the law, a practice that both Democrats and Republicans have pursued since it was enacted under Theodore Roosevelt.
The issue has been a particular flashpoint in the West, where some residents believe the federal government already imposes too many restrictions on development and others, including tribal officials, believe greater protections of ancient sites are needed.
Even before Trump made the announcement as part of a day trip to the state, National Cattlemen’s Beef Association president Craig Uden was hailing the resized designations. While grazing has continued on both monuments, as well as on others, Uden said ranchers could not have greater input into how they are managed.
‘‘We are grateful that today’s action will allow ranchers to resume their role as responsible stewards of the land and drivers of rural economies,’’ he said.
Republicans at the president’s rally applauded him and his deputies for heeding their concerns. ‘‘President Trump listened to us,’’ Utah House Speaker Greg Hughes said. ‘‘We are not a flyover state.’’
But a series of protests that opponents began over the weekend, attracting thousands, continued Monday at the Utah Capitol. About 300 demonstrators gathered before Trump arrived and, against the backdrop of the dome and snowy grounds, chanted ‘‘Lock him up!’’
Conservation advocates and tribal representatives have for months been preparing briefs that aim to block the monument changes in federal court.
Doug Wheeler, a partner at the firm Hogan Lovells who represents the Conservation Lands Foundation, Utah Diné Bikéyah, and other groups, said the ‘‘watershed’’ moment on this issue came with the 1976 Federal Land Policy and Management Act.
‘‘Congress made very clear, as a matter of law, that they intend to delegate only that which has been expressly delegated in terms of management of federal lands,’’ he said, adding that would mean a president can establish a monument under the Antiquities Act but not ‘‘rescind or substantially reduce’’ a site, he added.
Despite this legal uncertainty, Trump and his deputies have worked to address the concerns raised by Utah politicians such as Republican Senator Orrin Hatch and executives in the mining, ranching, and oil and gas industries.
A senior White House official, who spoke on the condition of anonymity to discuss internal deliberations, said the push to change the monument designations was driven by Hatch, House Natural Resources Committee chairman Rob Bishop, a Republican of Utah, and Interior Secretary Ryan Zinke.
The aide said the president appreciates Hatch’s work on the Senate’s tax overhaul bill, the aide added, and is hoping the 83-year old incumbent will run for reelection next year rather than provide an opening for Trump political rival Mitt Romney.
In April, Trump signed an executive order instructing Zinke to review more than two dozen monuments, and he tailored the document so it would include Grand Staircase-Escalante, which Bill Clinton designated in 1996.
In August, Zinke submitted a report to the White House that called for reducing at least four sites and changing the way at least a half-dozen others are managed.
In addition to Grand Staircase-Escalante and Bears Ears, which Barack Obama designated a year ago, Zinke recommended downsizing Oregon’s Cascade-Siskiyou and Nevada’s Gold Butte national monuments.
Zinke has also proposed more access for people and industry at other monuments.