1. On May 18, 1901, the South Dakota State School of Mines was established in Rapid City. Today, the school is known as the South Dakota School of Mines and Technology and is a leading engineering and science university in the country.

2. In 1927, on May 18, the South Dakota state legislature passed a law creating the South Dakota Highway Patrol. The patrol's primary mission was to enforce traffic laws and ensure public safety on the state's highways.

3. On May 18, 1953, South Dakota Governor Sigurd Anderson signed a bill establishing the South Dakota State Highway Commission. The commission was tasked with planning, constructing, and maintaining the state's highways and bridges.

4. In 1980, on May 18, The Mount St. Helens eruption occurred in Washington State. The volcanic ash cloud from the eruption reached South Dakota, causing damage to crops and affecting air travel in the region.

5. On May 18, 2013, the Crazy Horse Memorial in the Black Hills of South Dakota held its annual Volksmarch event. The event allows visitors to hike up to the top of the monument to see the progress of the ongoing construction of the monument honoring the Lakota leader Crazy Horse.