S.D. Codified Laws § 7-1-45

Beginning at the intersection of the range line between ranges sixty-five and sixty-six west of the fifth principal meridian, with the boundary line between the states of South Dakota and North Dakota, thence west and along said state line to the northwest corner of township one hundred twenty-eight north of range seventy-three west of the fifth principal meridian; thence south and along said range line between ranges seventy-three and seventy-four west, to the southwest corner of township one hundred twenty-five north of range seventy-three west; thence east and along the sixth standard parallel north, to the southeast corner of township one hundred twenty-five north of range sixty-six west; thence north and along the range line between said ranges sixty-five and sixty-six, to the place of beginning.