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Geology
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Generalized Geologic Map of the Conterminous United States
North America Shaded Relief
 

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  The North American Tapestry of Time and Terrain

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Legend and Rock Ages
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  Legend and Rock Ages
 

Proterozoic Rocks - 2.5 billion to 540 million years ago

map of Proterozoic rocks

 

The Proterozoic was a time in which multicellular algae began to appear. The continents grew in size and oxygen began to build up in the atmosphere. Today, Proterozoic rocks are found in features like the Superior Upland, the Black Hills, the Llano Uplift, and the Adirondack Mountains.

The Proterozoic has been divided here into the following (youngest to oldest):
Late Proterozoic
Middle Proterozoic
Early Proterozoic