<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> <P> Wetter climates brought upon by ice ages starting 2 million years ago greatly increased excavation of the Grand Canyon, which was nearly as deep as it is now, 1.2 million years ago . Volcanic activity deposited lava over the area 1.8 million to 500,000 years ago . At least 13 lava dams blocked the Colorado River, forming lakes that were up to 2,000 feet (610 m) deep . The end of the last ice age and subsequent human activity has greatly reduced the ability of the Colorado River to excavate the canyon . Dams in particular have upset patterns of sediment transport and deposition . Controlled floods from Glen Canyon Dam upstream have been conducted to see if they have a restorative effect . Earthquakes and mass wasting erosive events still affect the region . </P>

Where was the material that was eroded by the colorado river deposited