Dating the rocks of the grand canyon

The Great Unconformity is one of the best examples of an exposed nonconformity, which is a type of unconformity that has bedded rock units above igneous or metamorphic rocks.

The intrusion of the granite occurred in three phases: two during the initial Vishnu metamorphism period, and a third around 1.4 billion years ago.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.The new river captured the older drainage to form the ancestral Colorado River, which in turn started to form the Grand Canyon.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.