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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
 

Cambrian Rocks - 540 to 505 million years ago

map of Cambrian rocks

 

The Cambrian is a period famous for its "explosion" of diversity in aquatic animal life. The first animals with hard skeletons appeared during this period. The most famous Cambrian rocks may be the Burgess Shale in the Canadian Rockies, which contain the rare fossils of soft-bodied animals.

Beside the Burgess Shale, Cambrian rocks are also present in features such as the Driftless Area and the Appalachian Valley and Ridge Province.