## Facts

- An 1858 treaty established the Yankton Sioux Reservation in present-day South Dakota.
- Under federal allotment policy, tribal members received individual allotments; remaining unallotted “surplus” lands were negotiated for disposition.
- In an 1892 agreement, the Tribe agreed to “cede, sell, relinquish, and convey” all unallotted reservation lands to the United States for a fixed payment of $600,000.
- The agreement included a saving clause stating it would not be construed to abrogate the 1858 treaty and that treaty provisions would remain in force.
- Congress ratified the 1892 agreement through an 1894 Act, after which non-Indians rapidly acquired the ceded lands.
- In the early 1990s, a regional entity selected a site for a solid-waste landfill on unallotted, non-Indian fee land located within the original 1858 reservation boundaries.
- The Tribe and the United States asserted the site remained within the reservation and subject to federal environmental regulation; South Dakota asserted the 1894 Act diminished the reservation, leaving the site outside “Indian country” and under state jurisdiction.
- The federal district court declined to enjoin the landfill but declared the 1894 Act did not change reservation boundaries; the Eighth Circuit affirmed.

## Issues

1. Whether the 1894 Act ratifying the 1892 agreement diminished the Yankton Sioux Reservation by removing the ceded unallotted lands from reservation status.
2. Whether the landfill site on ceded, unallotted, non-Indian fee land is “Indian country” under 18 U.S.C. § 1151(a), affecting which sovereign has primary regulatory jurisdiction.

## Decision

- The Supreme Court unanimously reversed the Eighth Circuit.
- The Court held that Congress intended to diminish the Yankton Reservation through the 1894 Act.
- The ceded unallotted lands did not retain reservation status and therefore are not “Indian country” under 18 U.S.C. § 1151(a).
- South Dakota has primary jurisdiction over the landfill site and the ceded unallotted area.

## Legal Principles

- Reservation diminishment depends on congressional intent, assessed primarily through the text of the surplus-land statute, informed by contemporaneous historical evidence and subsequent demographic and jurisdictional history.
- Operative cession language (e.g., “cede, sell, relinquish, and convey”) coupled with fixed-sum compensation is strong evidence that Congress intended to diminish reservation boundaries.
- A saving clause preserving treaty “provisions” may preserve treaty rights but does not, without clear territorial language, negate statutory indicators that reservation boundaries were reduced.
- Subsequent demographic patterns and governmental jurisdictional practice may confirm, but cannot alone establish, congressional intent to diminish.

## Conclusion

The Court concluded that the 1894 Act implemented a total cession of the Tribe’s unallotted lands for fixed compensation, reflecting Congress’s intent to diminish the reservation; as a result, the landfill site on ceded unallotted land lies outside “Indian country,” and South Dakota possesses primary jurisdiction.


South Dakota v. Yankton Sioux Tribe, 522 U.S. 329 (1998)