James St. John > Collections

Northern Arizona's Grand Canyon is the "largest hole in the world". Almost 2 billion years worth of Earth's history is on display here.

The oldest rocks are at the bottom of the stack of layers, along the Colorado River. The Inner Gorge has Proterozoic igneous and metamorphic rocks, nonconformably capped by slightly tilted sedimentary rock layers of the Grand Canyon Supergroup (also Proterozoic). Most of Grand Canyon's walls consist of Paleozoic-aged, ~horizontally-oriented sedimentary rocks. These range in age from Cambrian to Permian.

The Grand Canyon is located in the Colorado Plateau Physiographic Province. After the Permian, the Colorado Plateau area was generally stable, but surrounding areas of western America were subjected to multiple episodes of orogenesis (mountain building). Uplift of the Colorado Plateau occurred during the Cenozoic. This involved 5,000 to 10,000 feet worth of tectonic uplift, although the rocks were not significantly deformed. Erosive downcutting of the Colorado Plateau by the Colorado River and its tributaries resulted in the majestically scenic "canyon country" of southern Utah and northern Arizona. The Grand Canyon is the best and biggest of the many canyons in this part of the world.