S.D. Codified Laws § 7-1-35
Beginning at the northeast corner of township one hundred sixteen north of range seventy-one west of the fifth principal meridian, thence west and along the fourth standard parallel north, to the northwest corner of township one hundred sixteen north of range seventy-three west; thence south and along the tenth guide meridian west to the center of the main channel of the Missouri River; thence down the center of the main channel of the Missouri River to its intersection with the second standard parallel north; thence east and along said parallel to the southeast corner of township one hundred nine north of range seventy-one west; thence north and along the range line between ranges seventy and seventy-one west, being the tenth guide meridian west, to the place of beginning.
SDCL 7-1-35