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Generalized Geologic Map of the Conterminous United States
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  The North American Tapestry of Time and Terrain

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  Legend and Rock Ages
 

Quaternary Rocks - 1.8 million years ago to the present

map of quaternary rocks

 

The Quaternary is the period in which we live, and it includes the Pleistocene and Holocene. The Quaternary is marked by a number of major climatic shifts, notably numerous ice ages. The last major ice age was less than 20,000 years ago, and at that time, glaciers reached as far south as Tennessee and Missouri.

The major tectonic activity in North America is along its western margins, as the North American plate interacts with the Pacific Plate. Much of the boundary is represented by the sliding action seen on the San Andreas Fault, but there are also regions of subduction, where the Pacific Plate is moving beneath the North American plate, creating features like the Aleutian Islands.