SALT LAKE CITY — President Barack Obama expanded his environmental legacy in the final days of his presidency with national monument designations on lands in Utah and Nevada that have become flashpoints over use of public land in the U.S. West.

The Bears Ears National Monument in Utah will cover 1.35 million acres in the Four Corners region, the White House announced Wednesday. In a victory for Native American tribes and conservationists, the designation protects land that is considered sacred and is home to an estimated 100,000 archaeological sites, including ancient cliff dwellings.

It’s a blow for state Republican leaders and many rural residents who say it will add another layer of unnecessary federal control and close the area to new energy development, a common refrain in the battle over use of the American West’s vast open spaces. Utah’s attorney general vowed to sue.

In Nevada, a 300,000-acre Gold Butte National Monument outside Las Vegas would protect a scenic and ecologically fragile area near where rancher Cliven Bundy led an armed standoff with government agents in 2014. It includes rock art, artifacts, rare fossils and recently discovered dinosaur tracks.

The White House and conservationists said both sites were at risk of looting and vandalism.

“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,” Obama said in a statement.

Obama’s creation and expansion of monuments over the course of his eight years in office covers more acreage than any other president.

His administration has rushed to safeguard vulnerable areas ahead of President-elect Donald Trump’s inauguration. It has blocked new mining claims outside Yellowstone National Park and new oil drilling in the Arctic Ocean. Obama’s creation and expansion of monuments covers more acreage than any other president.

But Trump’s upcoming presidency has tempered the excitement of tribal leaders and conservationists, with some worrying he could try to reverse or reduce some of Obama’s expansive land protections.

Utah’s Republican senators vowed to work toward just that.

“This arrogant act by a lame duck president will not stand,” U.S. Sen. Mike Lee tweeted about Bears Ears, which is named for a set of rock formations.

Sen. Orrin Hatch said Obama showed “an astonishing and egregious abuse of executive power” and that “far-left special interest groups matter more to him than the people who have lived on and cared for Utah’s lands for generations.”

Christy Goldfuss, managing director of the White House Council on Environmental Quality, said the Antiquities Act that allows a president to create monuments does not give a president authority to undo a designation, a rule the courts have upheld. She acknowledged that Congress could take action, though.

Opponents agreed the area is a natural treasure worth preserving but worried the designation would restrict oil and gas development as well as residents’ ability to camp, bike, hike and gather wood.