S.D. Codified Laws § 7-1-8
Beginning at the northeast corner of township one hundred five north of range sixty-seven, west of the fifth principal meridian, thence west and along the township line between townships one hundred five and one hundred six north, to the center of the main channel of the Missouri River; thence southerly and down the center of the main channel of said Missouri River to the base line between townships one hundred and one hundred one north; thence east and along said base line to the southeast corner of township one hundred one north of range sixty-seven west; thence north and along the range line between ranges sixty-six and sixty-seven west, to the place of beginning; and also that tract or parcel of land lying and being in the Missouri River and known as American Island.
SDCL 7-1-8