South Dakota’s ‘Black Hills’ are one of the most unique geologic landmarks the state has to offer. But how they got their name may surprise you. The Black Hills were first formed in the era of the dinosaurs. Around 65-70 million years ago, during the Cretaceous period. The human history of the Black Hills isn’t as long as you might think. The first signs of civilization in the area go back to around 1743 when French explorers claimed the region for the country of France. Later the Sioux Indian tribes moved into the hills from Wisconsin and built a lasting culture there.