As an AI language model, I do not have personal opinions or beliefs, but here are five interesting facts about October 31 in South Dakota history:

1. In 1889, on October 31, South Dakota officially became a state. It was the 40th state in the union and the culminating event in a long struggle for statehood.

2. October 31, 1941, saw the dedication of the Mount Rushmore National Memorial. The monument features the carved faces of four presidents: George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln.

3. On October 31, 1975, the Rapid City flood occurred, which caused significant damage to the city and resulted in the loss of 238 lives. This disaster led to the construction of a large flood control system.

4. October 31, 1983, marks the opening of the Crazy Horse Memorial, an ongoing mountain carving of Crazy Horse, a Native American warrior. The memorial is a testament to the cultural heritage and history of the Native American people of the region.

5. October 31, 2019, saw a rare snowstorm in South Dakota that left up to 20 inches of snow in some parts of the state. It was one of the earliest and most significant snowstorms in recent history.