What is the test for establishing that an individual is still a member of a tribe at the time of the signing of a treaty?

Rights under a treaty vest with the tribe at the time of the signing of the treaty, Washington, 520 F.2d at 692, but Indians later asserting treaty rights must establish that their group has preserved its tribal status: "[t]reaty-tribe status is established when a group of citizens of Indian ancestry is descended from a treaty signatory and has maintained an organized tribal structure." United States v. Washington, 641 F.2d 1368, 1372-73 (9th Cir.1981) ("Washington II "), cert. denied, 454 U.S. 1143, 102 S.Ct. 1001 (1982). The group seeking to exercise treaty rights must show that it has maintained an "organized tribal structure," which in turn can be shown by establishing that "some defining characteristic of the original tribe persists in an evolving tribal community." Id. at 1372-73 (finding no tribal status for lack of "continuous separate, distinct and cohesive Indian cultural or political communities").