Neither the EPA nor Wyoming monitors air quality over the 2.2 million acres of the Wind River Reservation. But a new EPA ruling giving the reservation the right to monitor air has brought up old disagreements. Irina Zhorov for Al Jazeera America

RIVERTON, Wyo. — Look at a map of the pretty pocket of land in central Wyoming known as the Wind River Indian Reservation, and you’ll see towns strung like pearls on the lines of road that traverse the territory. At the southeast corner of the reservation lies Riverton. On the map, the town of 10,615 appears to be part of the shaded rectangle marking Indian Country, yet Wyoming has considered Riverton nontribal land for more than 100 years.

That may have to change. A technical ruling on air monitoring by the Environmental Protection Agency in December put the town in the reservation, an action that has awakened dormant racial tensions, inflamed an already uneasy relationship between Wind River and Riverton and raised questions about what the boundaries really mean.

The EPA’s main focus in the matter — air quality — has in many ways been relegated to the back burner.

“I don’t think anyone’s opposed to air quality,” said Ron Warpness, mayor of Riverton, who sees what he called “an ulterior motive” in the tribe’s request to the EPA: the “Natives would like to have their land back if at all possible.”

Wyoming Gov. Matt Mead was more forceful, calling the EPA’s action “outrageous,” directing his attorney general to appeal.

The mood on the reservation was different, where residents welcomed the chance to expand air monitoring and the federal nod in their direction. Two tribes reside on Wind River, the Northern Arapaho and the Eastern Shoshone.

“For us, to have our boundaries defined only really just gives back the land we already knew was there,” said Darwin St. Clair Jr. of the Eastern Shoshone Business Council.