<P> The geology of the Grand Canyon area includes one of the most complete and studied sequences of rock on Earth . The nearly 40 major sedimentary rock layers exposed in the Grand Canyon and in the Grand Canyon National Park area 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 . There are at least 14 known unconformities in the geologic record found in the Grand Canyon . </P> <P> Uplift of the region started about 75 million years ago during the Laramide orogeny; a mountain - building event that is largely responsible for creating the Rocky Mountains to the east . In total, the Colorado Plateau was uplifted an estimated 2 miles (3.2 km). The adjacent Basin and Range Province to the west started to form about 18 million years ago as the result of crustal stretching . A drainage system that flowed through what is today the eastern Grand Canyon emptied into the now lower Basin and Range province . Opening 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 . </P>

What does each layer of the grand canyon represent