Interior Secretary Ryan Zinke's recommendation for President Trump to shrink some national monuments opens up the possibility for new mining or drilling on federal land that would no longer be off limits.

Environmentalists who oppose reducing the monuments have expressed alarm that mining or other energy companies could rush into suddenly unprotected land to try to extract fossil fuels that they believe will worsen global warming.

But energy and public lands experts say the monuments Zinke is reportedly targeting don't have strong prospects for crude oil or natural gas.

That is true of the most contentious national monument reviewed by Zinke, Bears Ears in Utah, which former President Barack Obama designated just before leaving office.

The New York Times reported Friday that Zinke is considering a dramatic reduction to Bears Ears, from 1.35 million acres to about 160,000.

A recent study commissioned by the left-leaning Center for American Progress found that Bears Ears ranks in the 52nd percentile for oil and gas resource potential as compared with areas of comparable size throughout the West. Bears Ears ranks in the 68th percentile for mineral resources.

"The places they are looking at scaling back don't have extraordinarily high resource potential," said Matt Lee-Ashley, a senior fellow at the Center for American Progress, in an interview with the Washington Examiner.

"You don't see the big oil and gas companies clamoring to get in there [Bears Ears], and that's indicative of the resource potential not being outstanding," added Lee-Ashley, who is also a former deputy chief of staff at the Department of the Interior.

Charles Wilkinson, a professor of public land law at the University of Colorado, said Bears Ears does have significant uranium deposits.

Wilkinson is an adviser to the Native American tribes who lobbied for Bears Ears to become a national monument.

"Mining is a serious threat to Bears Ears," Wilkinson told the Washington Examiner. "It is true that the oil and gas deposits are not extensive. But it would be extremely destructive to have uranium mining take place in undisturbed land."

Kathleen Sgamma, president of Western Energy Alliance, an oil and gas industry group, agreed that companies have little interest in Bears Ears.

"These monuments don't have a lot of oil and gas in them," she said. "Companies have long given up. The oil and gas industry have largely been unaffected by monument designations so far."

Luke Popovich, vice president of external communications at the National Mining Association, also downplayed corporate ambitions for mining on monument land.

"We've looked at this and really don't see any significant impact," Popovich told the Washington Examiner. "We even have some companies favoring monument designations."

Zinke did not say Thursday upon submitting his monument review to the White House whether he thinks monument designations have unfairly constrained oil and gas drilling on public land. He did not make his review of 27 national monuments public.

But an executive summary he released contained some language expressing his intent to limit some national monuments.

In it, he expresses general concern about what he and some Republicans see as abuse of the process that allows presidents to unilaterally declare national monuments.

The Antiquities Act, signed into law by President Theodore Roosevelt in 1906, specifies that national monuments should cover "the smallest area compatible with proper care and management of the objects."

"No president should use the authority under the 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 in the two-page executive summary.

"Adherence to the act's definition of an 'object' and 'smallest area compatible' clause on some monuments were either arbitrary or likely politically motivated or boundaries could not be supported by science or reasons of practical resource management," Zinke added.

Allies of the Trump administration's quest to limit some public monuments insist that process is their primary concern.

Rep. Rob Bishop, R-Utah, the chairman of House Natural Resources Committee, said he is encouraging the Trump administration to work with Congress to change the Antiquities Act to give presidents less power over monuments.

"This debate is about process and rule of law," Bishop told reporters Thursday. "The oil and gas elements of this are minimal. Claims of all sorts regarding [interest in] mining potential and exploration of resources are exaggerated and more scare tactic than reality."

Bishop last year introduced legislation to conserve Bears Ears in Utah, but his bill would cover less land than what Obama established. His plan would have allowed energy development in certain areas.

A national monument designation prohibits prospective mining and drilling on the land, although existing leases for energy extraction are maintained.

"It is simply not true there is a conflict between conservation and energy development," Bishop said.

Lee-Ashley said regardless of the energy potential at Bears Ears and other monuments targeted for shrinking, some federal lands in the West are worth protecting.

"The reason for protecting is that open lands in the West are disappearing," Lee-Ashley said. "The pace of development is very high. It really is a race to save wild places in the region. That's why monuments and national parks are important, so they become a bulwark against having complete loss of natural areas that define the region."