Around Sioux Falls and surronding areas are large outcroppings of Sioux quartzite. It rises and falls in great formations and sheets in the land. It was once a popular building material as wood was scarce. It is among the oldest rock on Earth.
See this link for a quick and entertaining explanation of Sioux quartzite: http://siouxquartzite.com/what-is-sioux-quartzite/
See this link for more technical and scientific info: https://en.wikipedia.org/wiki/Sioux_Quartzite
This particular dressed block is from the Washington Pavilion in downtown Sioux Falls, SD. It was originally an exterior block near the top of the building when constructed in 1908. Since then, it had been covered over with later additions. When the building ceased to be a high school, it was extensively renovated to become the new art and science center.