Quake Lake, located West of Yellowstone NP. The lake was formed by an earthquake in 1959 which measured 7.3 on the Richter scale and caused an 80 million ton landslide which dammed the Madison River. The slide area is in the center of the photo. The landslide traveled down the south flank of Sheep Mountain, at an estimated 100 miles per hour, killing 28 people who were camping along the shores of Hebgen Lake and downstream along the Madison River. The earthquake is the largest known to have struck the state of Montana in recorded history.