Forged letters and flyers appearing at gas stations and post offices in tribal lands in Utah are spreading false information about a proposal to create a national monument that protects Native American land.

The proposed Bears Ears national monument, named for the Bears Ears Buttes in south-eastern Utah, would cover up to 1.9m acres of land that is culturally significant to Native American tribes. The land is considered sacred to tribe members, and it contains more than 100,000 archaeological sites and structures.

Supporters of the monument say the fake documents are an attempt to misinform Native Americans and undermine efforts to safeguard the land. Posted on bulletin boards, the documents include a fake letter from Sally Jewell, the interior secretary, stating that about 4m acres of the Navajo reservation willby rampant looting. He noted that grave sites were being dug up and the artifactstaken from them sold for pennies on the black market.

Map of the at the proposed Bears Ears national monument in Utah. Photograph: Handout

Jewell has so far remained quiet on whether the president will designate a new national monument this year.

In an April speech, Jewell announced that her cross-country trip this summer would include a stop in Utah, where she said there were “a range of conservation proposals – legislative and otherwise – to further protect public lands”. She did not mention the Bears Ears national monument proposal, but supporters say they remain hopeful.

Asked if Jewell would address the Bears Ears proposal, the Department of Interior spokesperson said: “The secretary of the interior is still