RIVERTON -- A federal judge has dismissed the Northern Arapaho Tribe's lawsuit against the state of Wyoming and Fremont County over a long-standing boundary dispute.

The tribe claimed that land around the city of Riverton was still part of the Wind River Indian Reservation for taxation purposes. Congress more than 100 years ago opened reservation land in the area to settlement by non-tribal members.

Judge Clarence Brimmer of Cheyenne dismissed the lawsuit Tuesday. He ruled the lawsuit couldn't proceed without the participation of the United States and the Eastern Shoshone Tribe. The two tribes share the Wind River Indian Reservation in central Wyoming.

While Brimmer ruled that both the federal government and the Eastern Shoshone were indispensable parties to resolving the issue, both refused to enter the Northern Arapaho's lawsuit.

Brimmer wrote that neither the Eastern Shoshone or the federal government could be forced to join the case because they're sovereign governments and hadn't consented to being sued.

Northern Arapaho leaders say they plan to appeal Brimmer's decision.

"We've been preparing for this," Harvey Spoonhunter, chairman of the Northern Arapaho Tribal Council, said in a statement. "The ruling is consistent with the judge's comments from the bench."

Norman Willow Sr., co-chairman of the tribal council, said the tribe will continue to defend the reservation boundary.

"For us, conceding jurisdiction is not an option," Willow said. "We owe it to future generations to fight for sovereignty."

Jodi Darrough, lawyer for defendant Fremont County Treasurer Scott Harnsberger, said the county was pleased with the outcome.

"This case doesn't disturb previous court decisions regarding reservation boundaries," Darrough said.

The city of Riverton had entered the lawsuit to protect its interests in tax revenues from the disputed property.

Mayor John Vincent said Wednesday the municipality is pleased with Brimmer's decision.

"Although the substantive issues that were presented in the case weren't decided, we do know that this type of case can't proceed without participation of all the affected parties," Vincent said.