c. 6.5 Million BCE

The Grand Canyon

Liquid water flowing over the surface of the Earth is a major force for geologic change. Over time, ocean waves can wear down the seashore, and rivers and streams can carve deep gullies and canyons into even the hardest continental bedrock. The formation of canyons, in particular, can be further accelerated if that rock is being uplifted and is thus more susceptible to fluvial (stream- and river-related) erosion. That is exactly the situation going on within one of the Earth’s most spectacular geologic structures, the Grand Canyon.

The main part of the Grand Canyon of the Colorado River is just under 300 miles (480 kilometers) long and up to 20 miles (32 kilometers) wide, running mainly through Arizona but also in parts of Nevada, Utah, Colorado, and Wyoming. At its deepest, the Canyon extends nearly 6,100 feet (1,860 meters)—more than a mile—above the raging river below. The canyon is perhaps most famous for its numerous colorful layers of sedimentary, volcanic, and metamorphic rocks, as well as the fact that nearly 2 billion years of Earth’s geologic history is exposed to view in the Canyon’s walls.

There is considerable debate among geologists about when the Grand Canyon actually formed. Parts of the Canyon system appear to have formed as far back as the late Cretaceous (70–65 million years ago), probably as part of the overall regional uplift that formed the modern Rocky Mountains and the Colorado Plateau. The general consensus among geologists, based on rock and fossil ages and other clues, is that older Canyon networks were merged with newer, deeper ones created by more recent erosion only about 5 or 6 million years ago. The Grand Canyon appears to be a relatively young feature.

People have lived around and especially within the Grand Canyon for thousands of years, using the water, vegetation, and animal life along the more temperate regions near and along the river as resources for survival in what is otherwise a harsh desert environment outside the Canyon itself. Modern civilization also uses the Canyon for resources, now focusing on generation of hydroelectric power, tourism, and ecological/geological studies.

The view from Yavapai Point across the Grand Canyon exposes nearly 2 billion years of Earth’s geologic record for detailed study.