S.D. Codified Laws § 7-1-10

Beginning at a point where the center of the main channel of Redwater Creek crosses the boundary line between the states of Wyoming and South Dakota, thence easterly and along the center of the main channel of said Redwater Creek to the intersection of the township line between townships seven and eight north Black Hills base line; thence east and along said township line to the southeast corner of township eight north of range nine, east Black Hills meridian; thence north and along the range line between ranges nine and ten east, to the northeast corner of township fourteen north of range nine east; thence west and along the township line between townships fourteen and fifteen north, to its intersection with the boundary line between the states of South Dakota and Wyoming; thence south along said state line to the place of beginning.