During the last ice age, a giant lake formed in Montana which was created by a natural glacial dam. When the glaciers retreated, the lake swelled and broke the dam. In the Willamette valley it left fertile topsoil at depths of up to 100 feet! The Missoula floods were out of control. I say floods because this amazing event happened more than once. They were even more amazing than the biblical flood, because they actually happened.

I found this to be very interesting, and was under the impression that this was what had caused the Willamette river to run south to north. I was also under the impression that north-running rivers were rare, until I saw this page. Apparently they are not. However the Willamette is special, because it is one of our country's most polluted places. I think of this every time I see someone waterski or swim in it.