S.D. Codified Laws § 7-1-28
Beginning at the intersection of the center of the main channel of the Cheyenne River with the sixth guide meridian, east Black Hills meridian, thence south and along said sixth guide meridian to the township line between townships two and three, north; thence east on said township line between townships two and three north to the range line between ranges twenty-five and twenty-six, east Black Hills meridian; thence south on said range line between said ranges twenty-five and twenty-six to the Black Hills base line; thence west on said base line to the range line between ranges seventeen and eighteen, east Black Hills meridian; thence north on the range line between said ranges seventeen and eighteen to the center of the main channel of the Cheyenne River; thence easterly and down the center line of the main channel of said river to the place of beginning.
SDCL 7-1-28