Bears Ears National Monument will shrink by 90 percent, and the Grand Staircase-Escalante National Monument to half its original size, President Trump announced today. The land remaining in these Utah monuments will be divided into multiple smaller sections — an unpopular move that could open once-protected land to fossil fuel extraction and put sacred sites and local species at risk. Native American tribes and conservation groups are preparing to fight back in court.

Outside the Utah State Capitol today, President Trump said that he will cut Bears Ears National monument in southeastern Utah — from 1.35 million acres to 228,784 acres, according to a White House statement. The remaining scraps will be sliced into two different sections named Indian Creek and Shash Jaa. Grand Staircase-Escalante will shrink to 1,006,341 acres from 1.9 million acres and will be chopped up into three different units. “I have come to Utah to take a very historic action: to reverse federal overreach and restore the rights of this land to your citizens,” Trump said.

We’ve known that these cuts were coming since September, thanks to a leaked memorandum that outlined the Interior Department’s four-month review of 27 national monuments. That memorandum, obtained by the Washington Post, proposed shrinking the borders of Bears Ears and Grand Staircase-Escalante in Utah, Cascade-Siskiyou in Oregon and California, and Gold Butte in Nevada. But the memorandum didn’t say by how much.

“This represents the largest rollback of protections on public lands and waters in history.”

Now, Trump has revealed the size of the cuts planned for Utah — and conservation groups, hunters, and native tribes in the area aren’t happy. “This represents the largest rollback of protections on public lands and waters in history,” says Dan Hartinger with the conservation group The Wilderness Society. “Over 2 million acres would be opened up to commercial exploitation in places that the public overwhelmingly supports protecting.”

“This is a dark day for conservation,” agrees Land Tawney, CEO of the outdoor recreation advocacy group Backcountry Hunters & Anglers. “We’re irate about this because these monuments were designated to protect special places really from development.” His organization is especially concerned that cuts to Grand Staircase Escalante could harm its population of bighorn sheep, a popular game animal.

In fact, fragmenting these habitats could kill off resident plants and animals more quickly than if they were left with a larger, continuous territory, says William Newmark, a conservation biologist with the Natural History Museum of Utah. “What is particularly disturbing about Grand Staircase Escalante is not only have they reduced its total area, but they fragmented it into three units,” he says.

“This is a dark day for conservation.”

The changes also put key archaeological sites in Bears Ears at risk, says Katherine Belzowski, an attorney for the Navajo Nation. “Bears Ears is kind of a twofold monument,” she says. “It’s protecting not only the archaeological sites in the area, but it’s also protecting the landscape, which is considered sacred.”

It’s not clear if President Trump’s actions today are legal. While the Antiquities Act of 1906 gives the president authority to designate national monuments, it doesn’t explicitly permit abolishing them, according to High Country News. In fact, previous presidents have only shrank national monuments a handful of times in the past — like Mount Olympus National Monument, which Woodrow Wilson cut to half its size.

The Navajo Nation is gearing up to sue, Belzowski says, along with the four other tribes who pushed for Bears Ears to be designated a national monument in the first place: the Ute Mountain Ute Tribe, Ute Indian Tribe of the Uintah Ouray, Hopi Nation, and Zuni Tribe. “This vast reduction leaves out so many of our sacred sites and landscapes,” Belzowski says. “And we intend to defend those.”