Grand Canyon

The Grand Canyon is a steep-walled gorge cut by the Colorado River across the Colorado Plateau in northern Arizona, roughly 446 kilometers long, up to 29 kilometers wide and more than 1,800 meters deep at its deepest. Its walls expose a near-continuous sequence of layered rock spanning almost two billion years of Earth history, from the roughly 1.75-billion-year-old Vishnu Schist basement rock at the bottom of the inner gorge up through younger sedimentary units, including the Tapeats Sandstone, Bright Angel Shale, Redwall Limestone and Supai Group, to the approximately 270-million-year-old Kaibab Limestone forming the canyon rim, each layer recording a different ancient sea, desert or river environment. The canyon itself is geologically young by comparison: most current geological understanding holds that the Colorado River began carving roughly its present course some 5 to 6 million years ago, after regional tectonic uplift raised the Colorado Plateau, with the river's cutting power combined with weathering and rockfall on the canyon walls progressively widening and deepening the gorge into the layered profile visible today. This entity documents the Grand Canyon specifically as a named geological formation shaped by fluvial erosion, a distinct facet from its treatment as a place and landform in the Geography Atlas.