Dramatic climate changes transformed this landscape, affecting plants, animals, and humans. In ancient times, large shallow lakes covered what is now the valley floor, and American Indians of the Clovis culture hunted great herds of large mammals, including the Columbian mammoth. As the climate became drier, the cool lakes and lush wetlands gave way to grasslands and forests, and mammoths became extinct. Bison antiquus, a huge bison species now extinct, survived longer in the slowly drying conditions, and Folsom-era hunters adapted their tools and techniques to the changing game and environment. For Stone Age hunters, pursuing large animals involved both anticipation and danger. Ancient bones and projectile points recovered by archeologists remain as reminders in the sand of the enduring struggles of people and animals to continue on in an ever-changing world. A significant archeological site within Great Sand Dunes National Park contained evidence of forty-nine Bison antiquus carcasses butchered by Folsom-era hunters about ten thousand years ago.