S.D. Codified Laws § 11-2-27
The board may by resolution as provided in § 11-2-25 prescribe such regulations not contrary to law or § 11-2-26, as it deems desirable or necessary to regulate and control, or reduce the number or extent of or bring about the gradual elimination of nonconforming uses, lots, or occupancies. However, in accordance with the provisions of § 11-2-26, any lawful use, lot, or occupancy of land or premises existing at the time of the adoption of the zoning ordinance may be continued, even though the use, lot, or occupancy does not conform to the provisions of the zoning ordinance. If the use, lot, or occupancy is discontinued for more than one year, the board may adopt, after notice by registered or certified mail to the property owners, an amortization schedule to bring about the gradual elimination of the nonconforming use, lot, or occupancy.
SDCL 11-2-27