S.D. Codified Laws § 7-1-36
Beginning at the northeast corner of township one south of range twenty-five east Black Hills meridian, thence west and along the Black Hills base line to the northwest corner of township one south of range eighteen east; thence south and along the range line between ranges seventeen and eighteen east, to the center of the main channel of White River; thence westerly and along the center of the main channel of said White River to its intersection with the fifth guide meridian west of the sixth principal meridian; thence south and along said fifth guide meridian to the township line between townships thirty-nine and forty; thence east and along said township line to the west boundary line of the former Rosebud Indian Reservation, thence north and along the boundary line of said Indian reservation to the center of the main channel of White River; thence east and along the center of the main channel of White River to the range line between ranges twenty-five and twenty-six east; thence north and along said range line to the place of beginning.
SDCL 7-1-36