Geologic activity over the last 490 million years has removed or covered up most of the Cambrian rocks of North America. Today, rocks of this age can be found below the surface in many places, and while many states have exposures of Cambrian rocks, they are generally smaller than exposures from other periods. Cambrian exposures can be found in areas like the Basin and Range (throughout the West), the Rocky and Appalachian Mountains, and in New England, as well as in Wisconsin and many other states. The world famous Burgess Shale occurs in Cambrian rocks exposed in the Canadian Rockies; trilobites can be found in Cambrian-age rocks in northwestern Mexico.
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