S.D. Codified Laws § 7-1-47
Beginning at the junction of the centers of the main channels of the Belle Fourche and Cheyenne Rivers, thence along the center of the main channel of the Cheyenne river to its intersection with the one hundred second meridian of west longitude; thence north and along said meridian to its intersection with the third standard parallel north; thence west and along said third standard parallel north to the range line between ranges nine and ten east Black Hills meridian; thence south and along said range line to its intersection with the township line between townships seven and eight north of the Black Hills base line; thence west and along said township line to the range line between ranges four and five east; thence south to the township line between townships three and four north; thence east to the southwest corner of township four north of range six east; thence south to the boundary line between Pennington and Meade counties; thence east and along the present boundary line between Meade and Pennington counties to the center of the main channel of the Cheyenne River; thence northeasterly and along the center of the main channel of the said Cheyenne River to the place of beginning.
SDCL 7-1-47