CHEYENNE, Wyo. (AP) _ The state of Wyoming is asking a federal appeals court to reject the U.S. Environmental Protection Agency’s determination that Riverton and surrounding lands remain legally Indian Country.

The state filed a brief with the 10th U.S. Circuit Court of Appeals in Denver late Monday challenging the EPA’s decision.

The federal agency last year announced that it had determined a 1905 federal law opening over 1 million acres of the Wind River Indian Reservation to settlement by non-Indians didn’t extinguish the land’s status as a reservation. The agency addressed the boundary issue in granting a request from the Northern Arapaho and Eastern Shoshone tribes to treat their joint reservation as a separate state under the federal Clean Air Act.

Wyoming Gov. Matt Mead said the EPA used incomplete facts and faulty legal conclusions in reaching its decision. The federal agency will file its reply brief in February, he said.

“The EPA set a dangerous precedent altering Wyoming’s boundary by administrative action,” Mead said Tuesday in a prepared statement. “I asked the Attorney General to challenge the EPA’s decision because it potentially impacts the state’s sovereignty.”

The state, together with Riverton and Fremont County, appealed the EPA decision early this year. The EPA early this year announced that it was administratively staying its decision pending judicial review.

A final decision that Riverton and surrounding lands remain legally Indian Country could have ramifications on a range of government operations including taxation, court jurisdiction, environmental regulation and schools.

Wyoming’s lawyers filed hundreds of pages of material with the appeals court, tracing the history of the creation of the Wind River Reservation and several actions by Congress over the years that the state maintains whittled down its size.

“Wyoming’s brief shows how the EPA misconstrued what Congress said in 1905 and explains what we have all known to be true for over 100 years _ the city of Riverton is not on the reservation,” Mead said.

Mead has said he believes it’s up to Congress to determine reservation boundaries. Federal courts elsewhere, however, have ruled that the EPA has the responsibility to make reservation-boundary determinations when it acts on such tribal-permit applications.

An attempt to reach an EPA spokesman on Tuesday for comment wasn’t immediately successful.

EPA spokesman Rich Mylott issued a statement shortly after the agency announced its decision last year saying the agency’s boundary determination “was based on a thorough evaluation of relevant statutes and case law, historical documents, the Tribes’ application materials, public comments, and input from federal agencies.”

Mylott said last year that the EPA, the Department of Justice and the Department of Interior were working with the tribes, the state and communities to identify and resolve any issues related to the reservation’s boundaries and ensure the protection of public health and the environment.

Kimberly Varilek, attorney general of the Eastern Shoshone Tribe, said Tuesday that she had no comment on the state’s brief. An attempt to reach a lawyer for the Northern Arapaho Tribe was not immediately successful.