The lawful use 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 nonconforming use is discontinued for a period of more than one year, any subsequent use, lot, or occupancy of the land or premises shall be in conformance with such regulation.
SDCL 11-6-39