Fort Berthold Reservation, 1851

Treaty of 1851

map: Fort Berthold Reservation, 1851, with label that the Fort Laramie Treaty of 1851 reserved for the Mandan, Hidatsa, and Arikara reservation about 12.6 million acres.

The Fort Laramie Treaty of 1851 specified the legal boundaries of the land of the Mandan, Hidatsa, and Arikara people. It contained an estimated 12.6 million acres.