The combination more accurately reflects the surface of the earth, the age of the rocks beneath it and how the landscape was formed for the past 2.6 billion years, says the USGS website.
The colors represent the ages of the rocks. The hot pink covering most of northern Minnesota is rock from the Cambrian period about 500 to 550 million years ago. See the “color legend” for a complete key.
To get an idea of what’s beneath your feet, click “description of features” to read about some of the highlights in the Great Lakes basin.
Like the “Driftless Area” in Southwestern Wisconsin. The terrain there is rougher because it wasn’t scraped smooth by glaciers.
In Michigan’s Lower Peninsula the ridges west of the “thumb” are glacial rubble piles, or moraines, of an extinct glacier.
And check out the extinct Teays river in Ohio that was buried by glacial debris about 2 million years ago.