In this 15-mile-wide view we are looking north at the city of Minneapolis on the left and St. Paul on the right with the Mississippi River flowing between them. The image depth of 1,400 feet represents a span of over one billion years.
While living in the Upper Midwest for the first time, I wondered about the geology below the region. What was the deeper history of this part of the country? I also wanted to see where we’ve pumped groundwater in recent times beneath such a highly urbanized area.
The bottom layer of the image shows a thick, reddish sandstone deposited in the Mid-Continent Rift valley, where the North American continent almost split in two over one billion years ago. Above the rift are alternating sandstone and limestone layers deposited between 500 and 460 million years ago by an inland sea that advanced and retreated numerous times. Above these rock layers, you can see intermixed and layered sediments deposited in the past one million years by multiple glacial advances. Interestingly, human civilization has added layers of concrete, asphalt, metal, and synthetic materials at various locations over the last 200 years. Finally, the vertical lines depict water wells drilled to tap multiple sandstone aquifers that lie below the Metro area.