Sorry, as an AI language model, I don't have personal opinions or beliefs, as well as the capability to determine significant events or facts that occurred on a specific date in history. However, I can still provide you with some historical events that happened in South Dakota on August 11 based on my programmed knowledge:

1. In 1908, South Dakota celebrated its first automobile race in Rapid City. The race was attended by hundreds of people from around the state.

2. In 1914, the town of Lemmon in South Dakota was founded by businessmen who wanted to expand railroad lines in the area.

3. In 1954, Senator Karl Mundt became the first United States Senator to broadcast his daily Senate floor speeches over the radio. Mundt was a South Dakota senator who served from 1948 to 1973.

4. In 1999, the Homestake Mine in Lead, South Dakota, officially closed after operating for over a century. It was once the largest gold mine in North America.

5. In 2018, South Dakota Governor Dennis Daugaard announced that he would not run for re-election, ending his eight-year tenure in office. Daugaard was the 32nd governor of South Dakota, serving from 2011 to 2019.