She noted that in 1874 and again in 1897, the tribes had agreed to sell land on the Wind River Reservation to the federal government and cede control of the territory.

But the 1905 deal was different. Instead of a single lump-sum payment, the federal government would open plots north of the Wind River for sale. Any areas that weren’t purchased would return to tribal control.

The Supreme Court has determined that if language in a law passed by Congress included clear reference to selling or ceding reservation land and the federal government paid tribes a lump-sum for the property, then the land is no longer part of a reservation.

The federal government and tribes argued that since no lump-sum payment was made in 1905, the reservation had not been diminished.

But Tymkovich ruled that while both clear language and payment confirmed that a reservation’s boundaries had been amended, a boundary could also be changed without both those conditions being present.

“[T]his presumption is not a two-way street,” he wrote.

Tymkovich found that the language of the 1905 agreement and the circumstances surrounding its approval was sufficient to show that both the tribes and Congress believed they were changing the boundaries of the reservation.