Glacial Lake Missoula
The horizontal lines etched into the hillside are evidence that a prehistoric lake once filled the valley. The parallel lines represent the ancient shorelines of Glacial Lake Missoula. The highest known shorelines are found at an elevation of 4,200 feet. If the lake existed at this level today, the top of Mt. Jumbo would be an island and the city of Missoula would sit beneath 950 feet of water.