S.D. Codified Laws § 7-1-32
Beginning at a point where the range line between ranges nine and ten east Black Hills meridian intersects the boundary line between the states of South Dakota and North Dakota, thence west and along said state line to the boundary line between the states of South Dakota and Montana; thence south and along said boundary line and the boundary line between the states of South Dakota and Wyoming to the township line between townships fourteen and fifteen north of the Black Hills base line; thence east and along the township line between said townships fourteen and fifteen to the range line between ranges nine and ten east Black Hills meridian; thence north and along the range line between said ranges nine and ten to the place of beginning.
SDCL 7-1-32