WASHINGTON — From the revered giant sequoias of the southern Sierra to the unbroken vistas of the Mojave Desert’s historic Route 66, five national monuments in California await a verdict by Thursday from President Trump’s interior secretary on whether they should be left alone, shrunk or eliminated altogether.

The California monuments have been swept up in an unprecedented review — ordered by Trump in April — to determine whether their protected status inhibits potential commercial use. They are among more than two dozen monuments nationally being scrutinized by Interior Secretary Ryan Zinke.

Across the U.S., there are 129 national monuments designated by presidents dating to Theodore Roosevelt under the 1906 Antiquities Act to increase protection of existing federal land, and none has ever been abolished. Not since President John F. Kennedy has any president tried to shrink a monument.

The current review involves monuments created by presidents going back to Bill Clinton. So far, Zinke has revealed that he is likely to propose slashing the size of the 1.35 million-acre Bears Ears monument in Utah and will leave unchanged six others, including the new Sand to Snow monument northeast of Palm Springs created by President Barack Obama.

The administration’s review has provoked outrage among Democratic lawmakers and environmental groups.

Sen. Dianne Feinstein, D-Calif., who had a strong hand in the designation of three desert monuments, is battling the administration over the issue.

“This is war,” Feinstein said in an interview. “This is our history.”

While Congress has the power to revoke or change monuments, there’s not much a Democrat in the minority party can do to prevent Trump from altering them. So the fight will have to play out in the courts, where Trump’s legal authority to act will be challenged.

In California, the monuments still under review are the 330,780-acre Berryessa Snow Mountain monument northeast of Santa Rosa; the 204,000-acre Carrizo Plain in San Luis Obispo County known for its stunning wildflower blooms but also containing oil and gas leases; the 346,000-acre San Gabriel Mountains monument in Los Angeles County; the 328,000-acre Giant Sequoia National Monument in Tulare County; and the Mojave Trails National Monument that includes the landmark stretch of Route 66.

Oregon’s Cascade-Siskyou National Monument, which crosses into California, is also under review.

Trump’s executive order calls for determining whether the monument designations lacked input from local and state officials and “other relevant stakeholders” when they were created or would prevent energy development or “otherwise curtail economic growth.”

California Attorney General Xavier Becerra promised in an 11-page letter to Zinke that he would immediately sue if any monument alterations are attempted in his state. A host of environmental groups pledges to do likewise.

Ryan Henson, senior policy director for CalWild, a California wilderness coalition, called the administration’s actions an “over-our-dead-bodies time.”

Although a president has the unilateral authority to create monuments, the Antiquities Act contains no provision for him to revoke a designation, and the 1976 Federal Land Policy Management Act explicitly prohibits the interior secretary from revoking or modifying a monument.

But the review has its defenders even in California, where public lands are overwhelmingly popular. One monument that by its name would seem most off limits — Giant Sequoia National Monument — has some local officials clamoring for a reduction in its size.

They say the monument, designated by President Bill Clinton in 2000, threatens the ancient sequoia groves by preventing the use of logging to thin conifers now choking the forests.

“It sounds very self-serving being that I work for a sawmill,” said Darren Mahr, timber manager at the Sierra Forest Products sawmill in Terra Bella (Tulare County). “But we drew a line around the forest hoping it would be safe, and instead we’ve put it at risk.”

A century of fire suppression has turned the forests from the open groves John Muir described into dense thickets of fir and pine, many killed by drought or beetles.

Tulare County Supervisor Stephen Worthley led a vote by the Board of Supervisors asking Zinke for the reduction to allow logging. He said the U.S. Forest Service lacks the money to do the controlled burns necessary to restore the forest’s health, and logging to thin the trees would pay for itself.

The 2015 Rough Fire took a greater toll on the monument than it should have because of the density, he said. Some of “the ancient trees that we should be trying to protect with everything within us died because of the fire intensity,” Worthley said. The groves “are in greater peril today than before the monument was created.”

In Southern California, Rep. Paul Cook, R-Yucca Valley (San Bernardino County), wrote a letter to Zinke, urging him to slash the 1.6 million-acre Mojave Trails National Monument by half a million acres. The monument is the centerpiece of three California desert monuments, including Sand to Snow and Castle Mountains, that Obama designated last year at Feinstein’s request.

The Mojave Trails monument protects the last unspoiled section of Route 66 and preserves a biological link between Joshua Tree National Park and the Mojave National Preserve.

If fulfilled, Cook’s request will aid a plan by a private company, Cadiz Inc., to pump billions of gallons of water from the desert aquifer underlying the monument to sell to Southern California cities. Cook also joined nine other California House members from both parties in a private letter in March urging Zinke to clear the way for Cadiz.

David Lamfrom, head of the California desert and wildlife program for the National Parks and Conservation Association, a conservation group, said Cook’s requested monument reductions “directly overlap with the Cadiz project.”

Zinke already has reversed Obama-era regulatory rulings blocking the project. Deputy Interior Secretary David Bernhardt is a former Cadiz lawyer and lobbyist, and his former law firm holds stock in Cadiz. Bernhardt also led a Trump transition team that placed Cadiz on a list of the nation’s 50 highest priority infrastructure projects.

The aquifer feeds rare desert springs that support plant and animal life, and the U.S. Geological Survey said Cadiz has greatly overestimated the aquifer’s natural ability to recharge itself. The National Park Service said the estimates are so out of bounds they “should not even be considered.”

“The public has to understand that this is the first major step toward destruction of Mojave Trails,” Feinstein said. She called the Cadiz project “a killer. I don’t trust these people.”

Both Cook and Feinstein had proposed legislation to protect Mojave Trails, Sand to Snow and Castle Mountains, but they never agreed on the exact boundaries, and so the legislation never made it through Congress. In frustration, Feinstein turned to Obama.

Cook told The Chronicle in a statement that the area he wants removed is not justified for monument status because it was never included in the legislation he or Feinstein crafted. He called the Cadiz issue “immaterial.”

The Yucca Valley congressman also asked Zinke to add the Castle Mountains monument to the review process. It’s unknown whether Zinke will do so. The 21,000-acre monument protects a rare high desert grassland and large Joshua tree forests. Cook said in his letter to Zinke that shrinking the monument would help a Canadian-owned gold mine.

The methodology Zinke is using for his monuments review remains murky. Interior spokeswoman Heather Swift said in an email that Zinke opened the process to a 60-day public comment period “in an effort to make the process transparent and give people a voice.” The department received 2.7 million comments, overwhelmingly in favor of the monuments.

Swift said Zinke has also “held dozens of meetings” with various groups, including “people and organizations who represent all sides of the issue.”

Zinke has visited eight monuments, but none in California.

David Myers, executive director of the Wildlands Conservancy, which purchased nearly 600,000 acres of the Mojave Desert and donated them to the federal government for protection, said he has invited Zinke to visit Mojave Trails, but never heard back. About 45,000 acres of donated land is in the area Cook wants removed.

Myers said the Mojave Trails monument is “really what keeps the desert intact, having that mega landscape that connects Joshua Tree National Park to the Mojave National Preserve. Otherwise you just have islands of protection in the desert.”

Jim Conkle, a Marine known as “Mr. Route 66” for his efforts to protect the historic road, said neither Cook nor his staff will talk to him. “They don’t answer my phone calls, my emails, I go over there to see them, they’re there, but they’re not there to me,” he said. “They don’t want anything to do with me. Because they know that I just want to sit down and say, ‘Why are you doing this?’”

Rep. Mike Thompson, D-St. Helena, who took former Interior Secretary Sally Jewell on two hikes in the Berryessa-Snow Mountain area to push its designation, said the monument review “looks like just another effort to erase anything President Obama did.” He said the monument vetting was exhaustive.

“The idea that they would come back and try to unwind that,” he said, “is just a colossal waste of time.”

Carolyn Lochhead is The San Francisco Chronicle’s Washington correspondent. Email: clochhead@sfchronicle.com Twitter: @carolynlochhead