S.D. Codified Laws § 7-1-59
Beginning at the intersection of the centers of the main channels of the Cheyenne and Missouri rivers, thence westerly and up the center of the main channel of the Cheyenne River to the sixth guide meridian east Black Hills meridian; thence south and along said guide meridian to the township line between townships two and three north, Black Hills base line; thence east and along said township line to the west line of the fifth principal meridian survey, being the west line of range seventy-nine west of the fifth principal meridian; thence north and along said range line to the north line of township one hundred eight north of range seventy-nine west of the fifth principal meridian; thence east and along said north line of township one hundred eight north, to the center of the main channel of the Missouri River; thence northerly and up the center of the main channel of said river to the place of beginning.
SDCL 7-1-59