Eight national monuments created in California over the past two decades will be reviewed under an executive order signed Wednesday by President Trump that second-guesses designations covering more than a billion acres nationwide.

The monuments in California cover huge swaths of desert, mountains, lakes and forests, including rare stands of ancient sequoia trees. The question of whether Trump can repeal any of the designations is likely to end up in court if the president tries to do so.

His order instructs the Interior Department to review all national monuments designated by presidents since 1996 that are at least 100,000 acres, including 265 million acres protected by President Barack Obama.

During a signing ceremony Wednesday, Trump called Obama’s monument designations a “land grab” and said the order is designed to “end another egregious abuse of federal power, and to give that power back to the states and to the people, where it belongs.”

It means 30 or so monuments nationwide could be subject to alterations in size, purpose or ways the land is used. The president ordered Interior Secretary Ryan Zinke to evaluate each site designation for its compatibility with the original intent of federal law and its effect on the public’s use and access.

Under the order, Zinke will consider public and official opposition to national-monument designations and recommend any modifications within 120 days.

Environmentalists and legislators who support the monuments reacted with outrage.

“We’re treating this as the opening salvo of a full-scale attack on national monuments,” said Dan Hartinger, deputy director of parks and public lands for the Wilderness Society. “Removing the protections would be the first step you’d need to opening them back up to extractive uses like oil, timber and commercial fishing.”

Zinke promised to uphold the 1906 Antiquities Act, which gives the president power to create national monuments on public lands, but said he agrees with Trump that the law should not be be used to restrict historic uses like farming, grazing, ranching, timber harvesting, fishing or motorized recreation.

“We feel that the public, the people affected, should be considered,” Zinke said.

Twelve monuments have been established in California since 1996, but only eight of them fall under the order: Berryessa Snow Mountain, which sprawls across Napa, Solano, Yolo and four other counties in Northern California; Giant Sequoia, in the Sequoia National Forest in the southern Sierra; Cascade-Siskiyou, in southwestern Oregon and northwestern California; Carrizo Plain in the southern San Joaquin Valley; San Gabriel Mountains, northeast of Los Angeles; Santa Rosa and San Jacinto Mountains, west of the Coachella Valley in Riverside County; and two desert monuments that were pushed by Sen. Dianne Feinstein, Sand to Snow and Mojave Trails.

“For Californians who love the West, there is a lot to fear,” said David Myers, executive director of the Wildlands Conservancy. “These are places where we camp, hike, hunt, fish, so an attack on one is an attack on all. The administration is not standing with the American people — they are standing with a small minority of companies that want to privatize our public lands.”

Several California legislators and conservationists were confident that at least some of the state’s monuments would pass muster, even under an administration that has made clear that commercial interests should play a larger role in the government’s environmental decision-making.

“Berryessa Snow Mountain is a textbook-perfect example of what a monument designation should look like,” said Rep. Mike Thompson, D-St. Helena, who persuaded Obama to designate a 100-mile swath of land stretching from the shores of Lake Berryessa to the flanks of Snow Mountain in 2015. “The business community in the area sent over 100 letters in support, and every board of supervisors passed resolutions.”

However, California’s desert national monuments could be in jeopardy. Obama protected 1.8 million acres in February 2016 at the behest of Sen. Dianne Feinstein, D-Calif., who championed the monument designations for years.

House Republicans opened an investigation in March 2016 into the desert monuments, claiming a “lack of transparency and consultation with local stakeholders.”

The stakeholders they were referring to included local miners, rock collectors, recreational-vehicle users and others who feared their use of the land would be curtailed. The California Off-Road Vehicle Association was initially concerned, but eventually acquiesced under Feinstein’s prodding.

“The federal agencies have been very engaged and very responsive to our concerns,” said Amy Granat, managing director of the Off-Road Vehicle Association, which is working with officials on management plans at the desert monuments and Berryessa Snow Mountain that would permit off-road vehicles.

Back to Gallery National monuments under siege by Trump include 8 in... 7 1 of 7 Photo: ROBYN BECK, AFP/Getty Images 2 of 7 Photo: David Lamfrom / National Parks Conservation Association 3 of 7 Photo: STEPHEN CROWLEY, NYT 4 of 7 Photo: LARRY DOWNING, REUTERS 5 of 7 Photo: Andy Murdock, Special to The Chronicle 6 of 7 Photo: Reed Saxon, Associated Press 7 of 7 Photo: Francisco Kjolseth, Associated Press













David Lamfrom, California desert director for the National Parks Conservation Association, defended the desert monuments as crucial wildlife corridors that also preserve the last open stretch of historic Route 66.

“The California desert monuments were the product of legislation and a really widespread, grassroots-focused community process,” Lamfrom said. “When the Trump administration reviews the California desert national monuments, they will find a community that strongly backs them and a business community that cares deeply about protecting them.”

The administration and Republican legislators are apparently determined to test their resolve.

The Antiquities Act “does not give the federal government unlimited power to lock up millions of acres of land and water, and it’s time we ended this abusive practice,” Trump said.

The act has been used by 16 presidents, half of them Republican, to protect natural and historic features, including Muir Woods National Monument. President Herbert Hoover used it to establish Death Valley as a national monument in 1933, and President Franklin D. Roosevelt designated Joshua Tree in 1936. Both later became national parks.

Obama was particularly gung-ho about the act, using it to protect more than 550 million acres in 34 national monuments, more than Presidents George W. Bush and Bill Clinton put together.

Trump’s review was prompted in part by Utah GOP Sens. Orrin Hatch and Rob Bishop, who strongly objected to Obama’s 2016 designation of the 1.35 million-acre Bears Ears National Monument in southeastern Utah.

The monument, named after a pair of buttes that rise above the Colorado Plateau, is the ancestral home of several American Indian tribes and features 100,000 archaeological sites, including ancestral Puebloan cliff dwellings. The two senators said far more land than necessary was set aside in the monument.

Utah’s congressional delegation was also highly critical of Clinton’s 1996 designation of the Grand Staircase-Escalante National Monument in their state, which explains why Trump’s order goes back 21 years.

No president has ever rescinded a national monument designation, and there is no provision in the Antiquities Act for reversal. Legal experts say shrinking or revoking a monument would have to be done through an act of Congress, but some Republicans believe Trump can do it unilaterally and should be willing to go to court if necessary to win that right.

Conservationists reject that notion, saying Trump’s order is not only unnecessary but harmful.

“What they are doing is undermining one of the United States’ most important conservation laws and politicizing national monuments in a way that they frankly don’t deserve,” said Ani Kame’enui, director of legislation and policy for the National Parks Conservation Association. “Public lands are owned by all Americans. By calling into question these sites, they are calling into question part of the American story that is manifested in these sites.”

Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com Twitter: @pfimrite