About 5 miles from where I live is a small state park called Erratic Rock. It is called that because of a cluster of glacial rocks that are sitting on top of a hill.
What is so big about this you may ask? The fact that those rocks came from Canada about 15000 years ago, in a giant ice floe flood.
In the Google map picture you can see the Willamette Valley discolorization from the surrounding land. This is where the water, ice, and boulders came to a stop.
It seems that there was this giant lake (sea) up in Canada and it was formed because an immense ice dam formed that held back the melting ice water.
Over a few thousand years, the weather started to warm up, and the ice dam began to melt. When it finally broke all that water, ice and rock came down a crack
in the Earth that later became the Columbia River. When it finally stopped, it flooded the Willamette Valley all the way from where Eugene is now to up by Portland.
This was about 150 miles long and 40 miles wide and 200 feet deep. When the water receded it left behind some of the boulders that washed down in the flood.
One of those boulders found a footing on a small hill, under the water, and then appeared as the water left. The soil that was carried into this valley made the
valley the most fertile region in Oregon. When the news got out in the 1830's about how crops grew here, and animals thrived here, the people in the south and
Midwest hooked up their wagons and were lead to Oregon via the Oregon Trail. All of that happened because of an ice dam 15000 years ago that collapsed.
For many years no one every thought much about that rock, until a geologist heard about it. He then tested the rock against known samples and found that it
came from Canada. Then the archeologists began to study the Columbia River area and found more rocks and they finally surmised what had happened.
Here are two pictures. The first is of the rocks themselves and the next is the Google Earth image of the Willamette Valley which still shows how the water and
debris spread out in the valley. It is the area circled in red toward the left side, with the Columbia river marked.