Since The Mammoth Site is so close to Wind Cave National Park, it's a must see when visiting the area. It's about 8 miles from Wind Cave so it's not too far to drive. It is approximately 26,000 years old and has one of the largest concentrations of Columbian mammoth bones discovered to date. Believed to have been a sinkhole fed by springs, it is the only in-situ (left-as-found) site for mammoth bones in America. Mammoths, giant short-faced bears and other animals entered the pond, became trapped as a result of the slippery, steep banks and died of starvation. So far, about 61 mammoths have been uncovered (58 Columbian and 3 woolly mammoths). It's still an active dig site, so you can view current excavations and see paleontologist and volunteers digging for bones.
The Mammoth Site is in Hot Springs, SD and costs $12 to enter the museum. It's indoors, which is a huge bonus, since it was about 100 degrees when we visited it. It only takes about an hour to see everything. I enjoyed it since I've never seen mammoth bones before. It was really cool to see.