The geological history of western North America can be viewed as four distinct plate-tectonic phases which consists of the rifting/open margin phase about 700 Ma (Late Proterozoic) until 400 Ma (Middle Devonian) the ocean and island subduction zone, and the subduction Collisional/Orogenic phase about 180 Ma (Early Jurassic), and finally Post-Collisional phase commenced during the Early Tertiary. Some of the index fossils related to specific geology time which were found in each formation are presented.
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