Did you know that the ground upon which Corvallis now stands was previously on the bottom of a series of lakes, each of them formed when a dam burst up in Montana?
The dam in question was actually a glacier, one small part of the last Ice Age. It blocked the flow of the Columbia River, causing its waters to form Lake Missoula, a body of freshwater that commanded 3,000 square miles – larger than all of the modern Great Lakes combined. Eventually, the ice dam broke, and Lake Missoula drained as an immense flood, rushing down the Columbia Gorge in a torrent – one small backwash of which filled up the Willamette Valley and turned it into Lake Allison.
A few hundred years later, the glacier expanded and once again dammed up the Columbia, allowing Lake Missoula to fill up while Lake Allison drained. A few hundred years after that, the ice melted and, you guessed it, the dam burst again. Lake Missoula drained, and the Willamette Valley became Lake Allison. Noticing a trend here?
Having happened several times, each time a thick layer of mud was deposited on the valley floor. That’s why the Willamette Valley is mostly flat: it’s carpeted in soil washed away from Montana and Washington.
Those two neighboring states show it, as well. The region downstream of where Lake Missoula used to be in Washington is known as the Channeled Scablands, and it’s almost entirely jagged rock without any soil at all. During the cycle described above, most of it ended up washing out right out into the Pacific, with a little bit spared for the Willamette floor.
As far as we know, there were no humans living in the New World at that time. If there were, they’d probably have found the Willamette Valley as an inviting place to live, and then would have been completely wiped out when Lake Missoula flooded. For that matter, people living on the shores of Lake Missoula would have suffered terribly when their lake went away as well.
Of course, we can’t discuss this topic without mentioning Corvallis, Montana, which is hundreds of miles from Corvallis, Oregon. You’ve probably never been there. However, there are some boulders near our Corvallis that were washed here from the vicinity of Corvallis, Montana. Yes, boulders. These were quite big floods.