Trump's executive order authorized Zinke to review federal lands designated by Presidents Bill Clinton, George W. Bush and Barack Obama, setting up a possibly historic decision that would make Trump the first president to shrink a national monument. The preliminary report is the first step of a larger review of more than two dozen national monuments that protect USA public lands, mostly in the West.
"The previous administration used a 100-year-old law known as the Antiquities Act to unilaterally put millions of acres of land and water under strict federal control", Trump said of Obama's decision to protect the Utah land.
Zinke declined to quantify the area of the proposed smaller monument but said that the new boundaries should be limited to "the smallest area compatible" with the management of those sites.
Zinke visited Bear Ears in May, meeting with different stakeholders in the fight over Bears Ears, including a host of Native American tribes who have long viewed parts of the land sacred. Zinke recommended that Trump roll back the boundaries, to protect only areas that include historic and prehistoric structures, such as archaeological sites and remains of dwellings.
The report, provided to CNN, suggests revising aspects of Bears Ears' boundaries but does not detail where those changes would be made.
"That's a slap in the face of Native Americans", said Mark Maryboy, a former San Juan County commissioner.
Ethel Branch, Navajo Nation attorney general, said the lands within Bears Ears are essentially holy lands that hold critical plants, minerals and powers that members of many tribes rely on to heal and strengthen themselves.
"There is no doubt that it is drop-dead gorgeous country and that it merits some degree of protection", Zinke said.
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Utah rancher Zeb Dalton was among monument critics who wanted Zinke to recommend rescinding the entire monument. Whiteskunk said she was "appalled" at the announcement to try to reduce the monument's size.
On Monday, Zinke told reporters he didn't hastily come to his recommendation, but rather came it after traveling the land "by air, by vehicle, by foot and by horseback".
The Department of the Interior's public comment period for the national monuments under review - including Mojave Trails and Sand to Snow - closes July 10.
The department will also review the designations attached to five marine reserves including the Papahanaumokuakea Marine National Monument, which is the largest such marine reserve in the world.
Conservation groups, meanwhile, have called Trump's effort to alter existing national monuments illegal and irresponsible, and have vowed to challenge him in court.
Instead of the monument designation, which prevents a range of development, Zinke said some of the sprawling, 1.3 million acre site should be designated for conservation or recreation. "If carried out, these recommendations would shortchange current and future generations of Americans the opportunity to see an unspoiled and celebrated Bears Ears National Monument". The Republican-controlled Congress has failed to approve a significant public lands bill in recent years, but Zinke said that was because of veto threats by Obama.
Zinke said he will give a final recommendation, with specifics regarding acreage, when he has completed his review of the other monuments, as directed by the presidential executive order.
Associated Press writes Brady McCombs in Salt Lake City contributed to this story.