The geology of the Grand Canyon area exhibits one of the most complete and studied sequences of rock on the planet. The nearly 40 major sedimentary rock layers exposed in the Grand Canyon range in age from about 200 million to nearly 2 billion years old. Most were deposited in warm, shallow seas and near ancient, long-gone sea shores in western North America. Both marine and terrestrial sediments are represented, including fossilized sand dunes from an extinct desert. Uplift of the region started about 75 million years ago led to a mountain-building event that was largely responsible for creating the Rocky Mountains. In total the Colorado Plateau was uplifted an estimated 2 miles.
The formation of the Gulf of California around 6 million years ago enabled a large river to cut its way northeast from the gulf. The new river captured the older drainage to form the ancestral Colorado River, which in turn started to form the Grand Canyon.
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