1. Statehood Day: On September 1, 1889, South Dakota was officially granted statehood, becoming the 40th state in the United States.

2. Crazy Horse Memorial: On September 1, 1948, the construction of the Crazy Horse Memorial began in the Black Hills of South Dakota. The monument, which honors the legendary Lakota warrior, is still under construction and will be the world's largest mountain carving when completed.

3. Black Hills Gold Rush: The Black Hills Gold Rush began on September 1, 1874, when a military expedition led by George Armstrong Custer discovered gold in the area. This led to a rush of prospectors, miners, and settlers to the region.

4. Minuteman Missile Site: On September 1, 1991, the Minuteman Missile Site near Wall, South Dakota, was decommissioned. The site housed nuclear missiles during the Cold War and is now a National Historic Site.

5. Buffalo Roundup: The annual Buffalo Roundup in Custer State Park takes place on the last Friday of September, but preparations for the event begin on September 1. The roundup involves cowboys and cowgirls on horseback rounding up the park's approximately 1,300 buffalo so they can be counted, vaccinated, and sorted.