다시 보기 온라인 무료 보기. What strange forces saved one isolated section along the Upper Mississippi River from the repeated crushing and scouring effects of glaciers during the last two million years? And what pre-Ice Age throwbacks survived here in this unique geologic refuge that holds more Native American effigy mounds, petroglyph caves, strange geological features, and rare species than anywhere in the Midwest? These questions and more are answered in this captivating new documentary. A team of scientists embarks on a journey of exploration to expose both the science and threats behind three unique features of the zone - rare plants and animals, odd geological phenomenon, and striking remnants of a Native American pilgrimage like no other.