President Obama on Tuesday created new national monuments in a sacred tribal site in southeastern Utah and in a swath of Nevada desert, after years of political fights over the fate of the sites.

The designations further cement Obama’s environmental legacy as one of the most consequential — and contentious — in presidential history. He now has invoked his executive power to create national monuments 29 times during his tenure, establishing or expanding protections for more than 553 million acres of federal lands and waters. 

Environmental groups have praised the conservation efforts, but critics say they amount to a federal land grab. Some worry that the new designations could fuel another armed protest by anti-government forces inspired by the Cliven Bundy family, such as the takeover of the Malheur National Wildlife Refuge in Oregon this year.

Obama’s newest designations include two sprawling Western landscapes that are under threat, yet also where local residents are deeply divided on how the land should be used.

[Even from jail, the Bundys’ defiance still echoes in the Nevada desert]

In Utah, where the federal government owns roughly two thirds of the land, the designation of another 1.35-million acres to create the Bears Ears National Monument undoubtedly will prove polarizing. 

For the first time, Native American tribes will co-manage a national monument with the federal government. Five tribes that often have been at odds in the past — the Hopi, Navajo, Uintah and Ouray Ute, Ute Mountain Ute and Pueblo of Zuni — will together have responsibility for protecting an area that contains well-preserved remnants of ancestral Pueblo sites dating back more than 3,500 years.

“We have always looked to Bear’s Ears as a place of refuge, as a place where we can gather herbs and medicinal plants, and a place of prayer and sacredness,” Russell Begaye, president of the Navajo Nation, said in a call with reporters Tuesday. “These places -- the rocks, the wind, the land – they are living, breathing things that deserve timely and lasting protection.”

While many environmentalists and archeologists supported their monument, most Utah politicians opposed the site’s unilateral protection. Instead, House Natural Resources Committee Chairman Rob Bishop (R-Utah) and a fellow Utah Republican, Rep. Jason Chaffetz, devoted three years to drafting a land-use bill that would have protected a large portion of the site but would have allowed some development. The bill stalled in the House.

In a statement Tuesday, Chaffetz said he was “outraged” by the designation, saying Obama’s decision “politicizes a long-simmering conflict.”

“The midnight monument is a slap in the face to the people of Utah, attempting to silence the voices of those who will bear the heavy burden it imposes,” he said, vowing to work with the Trump administration to try to repeal the decision. “It does not have the support of the Governor, a single member of the state’s Congressional delegation, nor any local elected officials or state legislators who represent the area. 

Meanwhile, the Gold Butte National Monument in Nevada has been a site of contention for more than 15 years. As Las Vegas sought to expand, local, state and federal managers agreed to protect species such as the imperiled desert tortoise in Gold Butte. But they did little for either the animals or the actual sagebrush steppe and Mojave desert in the roughly 350,000-acre area marked by fossilized sand dunes and panels of petroglyphs that tower over the landscape. 

Though all the legal grazing permits in the area northeast of the Las Vegas were sold more than a decade ago as part of a deal with environmental groups and county officials, a single family — headed by cattle rancher Cliven Bundy — refused to recognize federal officials’ authority over the government land. The Bundys engaged in an armed standoff with Bureau of Land Management officials in 2014; several still await trial for the confrontation. Their followers occupied the Malheur refuge in January.

In a statement, Obama said Tuesday’s 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.”

[In Bears Ears, several tribes’ and Mormons’ origin stories collide]

Senate Minority Leader Harry Reid (D-Nev.), who has put more than 5 million acres of federal land in his home state off limits to development, pressed relentlessly for Obama to invoke his executive authority on behalf of Gold Butte. Reid intensified his campaign when the Bundys were jailed earlier this year for a takeover at the Oregon wildlife refuge, arguing that any pushback would be minimized while they were incarcerated.

“Gold Butte is a fascinating place full of natural wonders,” Reid said in a statement Tuesday. “Protecting Gold Butte ensures that generations of people will continue to have the opportunity to experience Nevada’s natural beauty. We’ve done something lasting and historic today.” 

Obama on Tuesday created both sites using his authority under the 1906 Antiquities Act, which gives president power to designate national monuments without approval from Congress. But the move could further inflame tensions with conservative Republicans, who are mulling changes to the law when they control both the executive and legislative branches next year.

How their effort fares could determine not only what safeguards persist for the landscape, rock carvings and other archeological sites in Bears Ears and Gold Butte, but what power future presidents can wield over the nation’s most ecologically and historically significant federal holdings.

Kristen Brengel, vice president of government affairs for the National Parks Conservation Association, said in an interview that she and others “just hope the American public rejects” efforts to curtail the act. Both Bishop and the congressman Donald Trump has tapped to head the Interior Department, Ryan Zinke (R-Mont.), support changes.

“It’s a wonderful law that allows the president to make quick decisions to protect areas when they need it,” Brengel said. “Why would we want to destroy that?”

BLM officials have documented acts of vandalism and looting in Bears Ears, but Bishop said he does not view it as being “in imminent danger.” He met on Dec. 5 with members of Trump’s transition team to discuss whether the next administration would consider overturning any designation Obama made in the area.

[Obama creates what could be the last large national park site on the East Coast, in Maine]

The Antiquities Act “does not prohibit a president from abolishing or modifying the terms of a previously declared monument which has not been ratified by Congress,” Bishop said in a statement after the meeting.

In a few instances, presidents have modified the size of monuments established by their predecessors: Woodrow Wilson slashed nearly half the acreage of Mt. Olympus National Monument, which Theodore Roosevelt had established. But in 1938, the U.S. attorney general wrote a formal opinion saying the Antiquities Act authorized a president to establish a monument but did not grant a president the right to abolish one. 

According to John Leshy, a former Interior solicitor general who now teaches at the University of California Hastings College of Law, neither the unilateral modification nor abolishment of a national monument “has been tested in court.” Congress, though, can potentially do both of those things. 

“We do not see that the Trump administration has authority to undo this,” Christy Goldfuss, managing director at the White House Council on Environmental Quality, said Tuesday.

Only Franklin D. Roosevelt has used the Antiquities Act more than Obama. And the president is likely to either match Roosevelt’s record with a 30th designation, according to several individuals briefed on the White House’s plans, or possibly to exceed it by doing two more before leaving office Jan. 20. 

Administration officials are eyeing an expansion of the California Coastal National Monument and Oregon’s Cascade-Siskiyou National Monument as well as the establishment of one monument in South Carolina and two in Alabama to commemorate the Reconstruction and civil rights eras, respectively.

[Obama designates the first-ever marine monument off the East Coast, in New England]

Yet given Republicans’ presidential and congressional victories last month, several proposals are likely to remain unrealized. Some activists are disappointed that Obama may not designate the Greater Grand Canyon Heritage National Monument, which would stretch more than a million acres and protect the area from new uranium mining. The monument has been supported by Native American tribes and, according to polling, a majority of Arizonans. But the state’s two GOP senators, John McCain and Jeff Flake, have so far opposed it, in part because of concerns it would prevent public access and complicate forest-thinning efforts necessary to prevent wildfire hazards. 

“I really feel the Grand Canyon is threatened,” said Arizona Rep. Raul Grijalva, the top Democrat on the Natural Resources Committee. Further development and mineral extraction can only become “more real” under a Trump administration, he fears. 

Grijalva noted that Congress has considered more than a dozen pieces of legislation aimed at curtailing, restricting or eliminating the president’s authority under the Antiquities Act. Until now, the threat of an Obama veto effectively blocked those efforts. That won’t be the case going forward. 

“That battle will come. I don’t see it going away,” Grijalva said. And it will set up a key question for Trump: “How willing is this new president to give up power?”