The monument preserves 206 pre European contact American Indian mounds of which 31 are effigies in the shape of bears and birds. A unique "Effigy Mound" culture developed in this area of the Upper Midwest placing thousands of mounds in the shape of animals across the landscape. Others are conical, linear or compound shapes; many of the conical are burial mounds. Eastern Woodland Indians built mounds from about 500 BC until the early European contact period. As a sacred site to the modern descendants of the moundbuilders, park access is offered via fourteen miles of hiking trails; no self guiding roadways exist in the park.