The 13-cent South Dakota State Flag stamp (Scott 1672) depicts the state flag adopted in 1963. From 1909 until 1963 images appeared on the flag's two sides. When it was decided to retain only one side, the designs were combined.
The state seal of South Dakota is centered on a sky blue field surrounded by the rays of the sun. Encircling the seal and the sun are the words "South Dakota" and "The Mount Rushmore State." The outer circle of the seal bears the words "State of South Dakota" and "Great Seal 1889."
The state seal represents South Dakota's commerce, industry, and natural resources. The state's motto—"Under God the People Rule"—appears over the inner circle. Within the circle is a background of sky and hills; a river runs through agricultural and industrial land; mining is represented with a smelting furnace; a steam ship plies the waters of the river; and a farmer plows a field against a backdrop of cattle and a cornfield.
Scott 2005 Specialized Catalogue of U.S. Stamps and Covers
SHG Resources (http://www.shgresources.com/sd/symbols/flag/)