Ron Dean, Hatch's Central and Eastern Utah Director, testified during a meeting in Utah of a state legislative public lands committee that he expects Bears Ears National Monument will be cut by at least 80 percent of its current size, while Grand Staircase-Escalante National Monument will be reduced by about 40 percent to 60 percent.
Trump told Hatch and Utah's governor last month that he would follow the recommendation of Interior Secretary Ryan Zinke and shrink both monuments, but the White House and Zinke's office have not offered details about how they'd redraw the monument boundaries.
Dean said Tuesday that while he hasn't seen Zinke's recommendations, he could speak with "some certainty" on how much of a reduction Hatch's office expected to see.
Utah's Republican leaders, including Hatch, have said the monuments declared by Democratic Presidents Barack Obama and Bill Clinton unnecessarily locked up too much land and asked Trump to shrink or rescind them.
The monuments were created under a 1906 law that allows presidents to protect sites that are considered historic, geographically or culturally significant. Trump ordered Zinke to review 27 monuments created under the law, with Bears Ears the top priority.
Bears Ears, which a coalition of tribal leaders spent years advocating for, covers about 1.3 million acres (5,300 square kilometers) of land considered sacred by Native Americans and home to thousands of archaeological sites, including cliff dwellings and petroglyphs.
Grand Staircase-Escalante, which includes about 1.9 million acres (7700 square kilometers) was named by President Bill Clinton in 1996.
Zinke's spokeswoman Heather Swift did not immediately respond to questions seeking details about Zinke's recommendations.
Zinke, who visited both monuments in May, told The Salt Lake Tribune on Monday that he thinks Bears Ears will end up larger than two existing national parks in Utah, keeping the monument at least 180,000 acres (728 square kilometers).
The plans for a dramatic reduction to the rugged spaces drew criticism Tuesday from U.S. Sen. Dick Durbin, the No. 2 Senate Democrat, after Zinke met with Durbin and four other Democratic senators.
Durbin said in a statement that he's concerned Trump plans to shrink Bears Ears by about 80 percent and called for Zinke to be more transparent and release maps of the proposed changes.
"It is clear that this decision is not based on protecting some of the most extraordinary natural resources in our nation, but rather on protecting political alliances," Durbin said.
Trump is expected to offer more details about his plans for the monuments when he visits Utah in early December.
Associated Press writer Matthew Daly in Washington contributed to this report.
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