Zinke's report, which the White House did not release, launches what will be a legal and political battle over a relatively obscure law that grants a president wide latitude in preserving federal lands and waters that are threatened.
After spending nearly four months examining more than two dozen monuments established by Bill Clinton, George W. Bush and Barack Obama under the 1906 Antiquities Act, Zinke is calling for less major change than some conservatives advocated. But in addition to radically shrinking Bears Ears and perhaps other sites, he is pushing to allow activities at some monuments that previous presidents restricted or barred outright.
"The recommendations I sent to the president on national monuments will maintain federal ownership of all federal land and protect the land under federal environmental regulations," Zinke said in a statement, "and also provide a much needed change for the local communities who border and rely on these lands for hunting and fishing, economic development, traditional uses, and recreation."
The review process was triggered by an executive order Trump signed April 26. It pitted those who have felt marginalized by federal actions over the past 20 years against backers who see the sites as bolstering tourism and recreation while safeguarding important relics, environments and species.
In his statement, Zinke described his proposal as a reasonable remedy to years of presidents' unilaterally exercising their authority without giving adequate consideration to the people living closest to these public lands.
"No President should use the authority under the Antiquities Act to restrict public access, prevent hunting and fishing, burden private land, or eliminate traditional land uses, unless such action is needed to protect the object," Zinke said.
Yet John Leshy, who served as Interior's solicitor in the Clinton administration and is now a professor at the University of California's Hastings College of Law, noted that no president had ever sought the kind of rollbacks Trump is contemplating.
"The scale of this, and the sweep of this, is definitely unprecedented," Leshy said.
Ethan Lane, executive director of the public lands council at the National Cattlemen's Beef Association, said the administration's push reflected that "they're concerned with rural America."
"They've been talking to groups that feel like maybe they weren't included in the process," Lane said. "Ranchers across the West are certainly part of that."
The Interior Department gave no specifics of Zinke's recommendations, instead releasing a report summary that described each of the 27 protected areas scrutinized as "unique."
Even so, his proposal takes direct aim at several, according to several individuals who asked for anonymity because the report has yet to be made public.
The most controversial site, the 1.35 million-acre Bears Ears, was designated by Obama last year. Zinke had called for revising its boundaries in an interim report in June, and he stayed with that in recommending a "significant" reduction in its size Thursday, an administration official said.
A White House official confirmed that Trump had received the report but would not say when it would be released or when the president would act on it.
Zinke's statement addressed the huge amount of public input the department received regarding the sites being scrutinized. "Comments received were overwhelmingly in favor of maintaining existing monuments and demonstrated a well-orchestrated national campaign organized by multiple organizations," he said.
He acknowledged supporters' point that monuments can bring economic benefits to local communities. But he also noted opponents' concerns that designations had translated into reduced public access, confusing management plans "and pressure applied [to] private land owners . . . to sell."
Zinke, who visited seven monuments as part of his review, did not recommend abolishing any. Over the summer he already had disclosed that six sites were no longer under scrutiny; an aide said there was little to no local opposition to each.
With the remaining monuments, some of the key constituencies most critical of sweeping restrictions on federal lands and waters — ranchers, fishing operators and local Republican politicians — won key concessions in the secretary's final set of recommendations.
Massachusetts Lobstermen's Association Executive Director Beth Casoni, who met with Zinke in Boston in June, wanted the administration to shrink the Northeast Canyons and Seamounts Marine National Monument "to the size of a postage stamp."
Within the monument's 4,913 square miles "is highly profitable, sustainable protein fishing ground" where Casoni said fishermen pursuing tuna, cod and sea bass and other fish have been barred. Under last year's proclamation by Obama, those working lobster and crab pots have seven years before having to pull them.
Environmental groups have made it clear that they will file legal challenges in an effort to preserve sites' existing boundaries and protections.
While Congress can alter national monuments easily through legislation, presidents have reduced their boundaries only on rare occasions.
Woodrow Wilson nearly halved the acreage of Mount Olympus National Monument, which Theodore Roosevelt had established six years earlier. In 1938, the U.S. attorney general wrote a formal opinion saying the Antiquities Act authorized presidents to establish a monument but did not grant them the right to abolish one, and several legal scholars argue that Congress indicated in the Federal Land Policy and Management Act of 1976 that it reserved the right to alter any existing monument.
Robert D. Rosenbaum, who serves as counsel to the National Parks Conservation Association, said Wednesday that no president has sought to shrink a monument's boundaries in the past four decades. "If the president attempts unilaterally to take adverse action on any of the monuments under review, he would be on very shaky legal ground, and we expect the action would be challenged in federal court," he said.
Sen. Maria Cantwell of Washington state, the top Democrat on the Energy and Natural Resources Committee, issued a scathing critique of the process the administration was using to scale back the designations.
"Teddy Roosevelt would roll over in his grave if he could see what Donald Trump and Ryan Zinke are trying to do to our national treasures today," she said. "Secretary Zinke's secret report to the president is the latest step in a rigged process to try and turn over our public lands to oil and gas companies."
Native American officials have lobbied hard to preserve Bears Ears, which boasts tens of thousands of archaeological sites as well as ancestral Pueblo rock art. Seven tribes in Utah and the Fort Peck Assiniboine and Sioux Tribes of Montana, which counts Zinke as an adopted member, passed resolutions this month calling for its boundaries to remain in place.
But many Western Republicans criticized such large protected areas as a distortion of the law's original intent. In a call with reporters Thursday, House Natural Resources Committee Chairman Rob Bishop (R-Utah) said that "Congress never intended one individual be given the power to unilaterally dictate land management policies for enormous swaths of public land."
"It's about how we protect our resources, not if we protect them," said Bishop, noting that Obama had applied his authority under the Antiquities Act to more than 550 million acres of land and sea. "That's just under 190,000 acres of land and water locked up for every day he was in office."
Utah has become a flash point for tensions over the law. With Grand Staircase-Escalante, Clinton's designation stopped a proposed coal mine and the jobs that would have accompanied it. Kane County Commission Chairman Dirk Clayson, whose county includes the monument, said in an interview Tuesday that "extreme conservation groups want to protect and tie up the land."
Nicole Croft, executive director of Grand Staircase-Escalante Partners, refuted such claims — in part by citing language in the monument's proclamation that, for example, specifically maintains existing permits for livestock grazing. She said commissioners "refused to even sit down at the table" with the monument's supporters or to acknowledge how it has helped to power the local economy.
In Cascade-Siskiyou on the Oregon-California border, ranchers have pushed back even as scientists and conservationists successfully lobbied to expand it to address climate change and other environmental threats. Clinton established the monument in 2000, and Obama expanded it to 113,000 acres in January.
The Klamath, Siskiyou and Cascade mountain ranges intersect within the monument, as do several distinct ecosystems that provide for a vast biodiversity of plant and animal species. Dave Willis, who chairs the Soda Mountain Wilderness Council, noted that a 2008 Bureau of Land Management study concluded that grazing was degrading the native habitat. His group has spent more than $1 million buying out ranchers' permits.
But John O'Keeffe, president of the Oregon Cattlemen's Association, said ranchers were under pressure to sell and had changed their practices over time. "We're doing a pretty darn good job now," he said.
Management changes the administration imposes on these protected sites may be as significant as any shifts in boundaries. Opponents of monuments, many of whom supported Trump, complained of being barred from grazing, drilling and hunting in some cases. Interior could provide more access for cattle, the oil and gas industry, vehicles and hunters.
At marine monuments, Zinke heard stakeholders complain about being denied access to rich troves of fish, lobsters and crabs.
William Aila, a Native Hawaiian fisherman and former chair of the state's Land and Natural Resources Department, said in an email that federal authorities had restricted commercial fishing in Papahanaumokuakea Marine National Monument for a reason.
"If commercial fishing is allowed, this administration is clearly listening to industry and putting dollars before common sense," he said.