Diminishment is the legal process by which the United States Congress can reduce the size of an Indian reservation.
In 1984, the United States Supreme Court held in Solem v. Bartlett, 465 U.S. 463 (1984), that "only Congress may diminish the boundaries of an Indian reservation, and its intent to do so must be clear.
[2] In the 1994 case Hagen v. Utah, 510 U.S. 399 (1994), the Supreme Court held that Congress's 1902 Act had diminished the Uintah Reservation.
Diminishment commonly refers to the reduction in size of a reservation.
A finding of diminishment generally suggests that a discrete, easily identifiable parcel of land has been removed from reservation status.