 That extraordinary pile of rock behind me is Hart Mountain. As impressive as it is, it's but a tiny fragment of one of the greatest landslides in Earth's history. Try to imagine yourself standing here in the northern Bighorn Basin near Cody when a block of carbonate and lava rock over a mile in height then 13 times the size of Manhattan Island breaks off a plateau near Yellowstone Park and travels towards you at speeds of about 100 miles per hour. The block that became Hart Mountain was near the leading edge of the slide and it was transported about 40 miles to its current resting place, possibly in just a few minutes. Now why do we think that? Well first, the rock on top of Hart Mountain is almost 300 million years older than the sediments that it now stands on. It had to have been a landslide. It came from near Cook City on the northeast corner of Yellowstone. During the landslide, the detached rock was broken into at least 50 large blocks of which Hart Mountain is the most prominent. Volcanic activity probably initiated the detachment. Well nobody knows exactly why the slide slid as far as it did, but whatever the combination of powerful forces combined to create it, Hart Mountain is an impressive Wyoming landmark and a geologic mystery that has found its way into the world's textbooks. From the University of Wyoming Cooperative Extension Service, I'm Eric Peterson exploring the nature of Wyoming.