President Obama protected two massive areas in the American West on Wednesday, including a swath of southern Utah that has been at the center of a contentious battle over land protections for years.

The areas newly protected from development and various activities are the Bears Ears National Monument in Utah and the Gold Butte National Monument in Nevada. Both areas are owned by the federal Bureau of Land Management.

The actions further cement the aggressive conservation legacy of Obama, who has protected more land and water than any other president under the Antiquities Act.

But the designations are among the most controversial under Obama, with strong opposition among local and state leaders.

Obama said in a statement that the designations “protect some of our country’s most important cultural treasures, including abundant rock art, archeological sites, and lands considered sacred by Native American tribes.”

“Today’s actions will help protect this cultural legacy and will ensure that future generations are able to enjoy and appreciate these scenic and historic landscapes,” he continued.

Obama created the designations using his unilateral authority under the Antiquities Act, acting with just about three weeks left before President-elect Donald Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE takes office.

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It’s unclear if Trump could unilaterally undo Obama’s designations, because it has never been tried before. Some Republicans, including House Natural Resources Committee Chairman Rob Bishop Robert (Rob) William BishopOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right House energy package sparks criticism from left and right OVERNIGHT ENERGY: EPA head questions connection of climate change to natural disasters | Pebble Mine executives eye future expansion in recorded conversations | EPA questions science linking widely used pesticide to brain damage in children MORE (R-Utah), say it is within Trump’s power, though the Obama administration says the Antiquities Act does not allow monument designations to be undone.

But the controversy surrounding Wednesday's actions, combined with Obama’s aggressive use of his Antiquities Act power, could lead Congress to roll back the protections or limit future presidents’ powers.

The 1.35 million-acre Bears Ears area could be the most controversial of Obama's dozens of national monuments, in part because it shuts down any new leases for mining or oil and natural gas, exploration, along with other development and potential harms.

Utah’s political leaders and its all-GOP congressional delegation oppose the national monument, and pledged before Wednesday’s announcement to seek action through Congress or Trump’s administration to undo the protections.

The monument protects numerous sites that are significant to nearby American Indian tribes for cultural, religious and historic reasons.

The tribes have long called for land protections in the area. The Utah congressional delegation has recently pushed a legislative package it calls the Public Lands Initiative to protect some areas and avoid a monument designation, although it never passed.

Christie Goldfuss, managing director of the White House Council on Environmental Quality, cited that proposal and others in recent decades as Obama’s guiding principles for the designation.

“The new monument responds to both of these recent proposals to include the areas where there is the strongest agreement about the need for protection, and to ensure that traditional uses and historical activities, including tribal acts, grazing and outdoor recreation can continue,” she told reporters.

Russell Begaye, president of the Navajo Nation, welcomed the Bears Ears designation, even though it is smaller than his tribe and others hoped for.

“This is an exciting day for the Navajo Nation, for our traditional leaders, for elected leaders across the Navajo Nation, and also the tribes that live in area who have always looked to Bears Ears as a place of refuge, as a place where we can gather herbs and medicinal plants and a place of prayer and sacredness,” he said.

But Sen. Mike Lee Michael (Mike) Shumway LeeMcConnell shores up GOP support for coronavirus package McConnell tries to unify GOP Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE (R-Utah) slammed Obama’s decision.

“This arrogant act by a lame duck president will not stand,” Lee tweeted Wednesday.

“I will work tirelessly with Congress & incoming Trump administration to honor the will of Utahns and undo this monument designation,” he added.

I will work tirelessly with Congress & incoming Trump administration to honor the will of Utahns and undo this monument designation. #utpol — Mike Lee (@SenMikeLee) December 28, 2016

Goldfuss said if that happens, it wouldn’t be through Trump’s executive authority.

“In terms of whether it can be overturned, no,” she told reporters. “The Antiquities Act gives the president the authority to create monuments, but does not provide explicit authority to undo them.”

The Nevada monument is also controversial, for different reasons.

The Gold Butte area is next to the ranch of Cliven Bundy and the site of an armed standoff between federal authorities and self-styled militia members in 2014.

The monument, pushed by outgoing Senate Minority Leader Harry Reid Harry Mason ReidThe Supreme Court vacancy — yet another congressional food fight Trump seeks to turn around campaign with Supreme Court fight On The Trail: Battle over Ginsburg replacement threatens to break Senate MORE (D-Nev.) among others, protects numerous tribal sites, important landscapes, rare fossils and more.

“Today’s designation will better protect these cultural and archeological treasures, as well as the areas that are currently used by tribes for traditional purposes,” Goldfuss said.