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


  The North American Tapestry of Time and Terrain

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Legend and Rock Ages
Rock Types
Political Boundaries

  Legend and Rock Ages

Triassic Rocks - 248 to 208 million years ago

map of Triassic rocks


A series of mountain-building events occurred along the western coast of North America during the Triassic, when all the continents were part of the supercontinent Pangea. These events were the result of oceanic plates subducting under the continent, carrying landmasses that collided with and attached to the continent, creating chains of Andes-like mountains. It was also during the Triassic that Pangea began to break apart. In the meantime, dinosaurs evolved and, as throughout the history of the planet, meteorites hit the Earth. One of the largest impact craters visible today, the Manicouagan crater, was formed in this period.

Later in the Triassic, the supercontinent of Pangaea began to break apart. The end of the Triassic is marked by a major extinction event that killed 20% of marine animals and many of the species on land that competed with the dinosaurs. With much of their competition gone, dinosaurs became the major land animals while the predatory ammonites proliferated in the oceans.