Geography
Northwestern Arizona is part of the arid Colorado Plateau. Sedimentary rocks here were uplifted horizontally. The dry environment made them susceptible to erosion.
History
About four million years ago, the Colorado River changed its course and began to cut through the layers of the present-day Grand Canyon. Winds, rain and runoff further eroded canyon walls and created side canyons.
Ice's Role
Although Arizona is known for dry, hot weather, ice plays a major role in canyon formation. When water seeps into cracks in the rock and freezes during the winter, it expands, pushing the rock apart.
Geological Significance
The Grand Canyon is an important resource for geologists. Its layers hold fossils and rocks that reveal three of the earth's four geological eras.
Age
The Grand Canyon is young compared with the layers of rock represented in its walls. The youngest layer, Kaibab limestone, is 250 million years old. The oldest, Vishnu schist, is 2.6 billion years old.
Size
These layers comprise the walls of the Grand Canyon, which average 4,000 feet deep and run for more than 277 miles.
Article Written By Kelly Aspen
Kelly Aspen's writing focuses on natural places, cultural sites and wildlife. She has nine years of experience as an editor and writer for magazines, books and websites, including Trails.com, Travels.com and Weekendnotes.com. She attended Vassar College and now lives in the mountains of Colorado.
