This video shows where the huge floods went through the western states of Washington, Oregon, and Idaho. According to the video, gigantic lakes were formed around the time of the ice ages, and as the water overflowed and escaped from the lakes, enormous boulders were carried along in the flood waters and dropped along the way as the water worked its way to the Pacific Ocean. As a believer in the young earth theory, I personally do not think that this happened millions of years ago; but that what they think happened over eons of time, actually happened in a much shorter time period, and as a result of the Noaic Flood. No matter what you believe about how this happened, the pictures and story are awesome to look at !
Lake Agassiz was a large glacial lake, larger than all of the Great Lakes combined, that covered much of Manitoba, northwest Ontario, northern Minnesota, eastern North Dakota, and Saskatchewan. They theorize that the melting of the remaining Hudson Bay ice caused Lake Agassiz to drain almost completely.