The Grand Canyon is one of America’s most beloved and well-known geographical wonders and is visited by millions of people every year. The canyon is a mile deep and up to 18 miles wide in places; it covers 277 miles over 1,217,403 acres of the Grand Canyon National Park and still is not the deepest canyon in the world (that award goes to the Kali Gandaki Gorge in Nepal).
The canyon complex contains artifacts from five Native American tribes that live there, the Colorado River and its tributaries, which formed much of the canyon, and other awe-inspiring formations and vistas.
How Old is the Grand Canyon?
The Grand Canyon as we know it has evolved over 3-6 million years through floods and climate changes, each event shaping and creating layers that have preserved the story of how it has been built by nature.
The unique erosion of the canyon walls allow geologists to see the individual layers of rock in addition to fossils and other matter that allow them to theorize about the age, creation, and continued evolution of the Grand Canyon.
Where is the Grand Canyon?
The Grand Canyon lies on the Colorado Plateau, which straddles the Four Corner states of Arizona, Colorado, Utah and New Mexico.
How Did the Grand Canyon Form?
The entire plateau contains sediment layers from the Proterozoic and Paleozoic Eras and is one of the unique physiographic sections of the plateau.
The entire Colorado Plateau experienced a physical uplift approximately 65 million years ago during a period called the Laramide Orogeny, prompting an increase in the elevation of the layered Plateau and the Colorado River’s stream gradient; these allowed the water in the Colorado River to run faster, erode quicker, and create the stunning geographical features viewed in the canyon today.
The additions of Lake Mead in 1936 and Lake Powell in 1963 from the building of the Glen Canyon and Hoover dams have also influenced the Colorado River’s speed, water levels, and eroding ability in the more recent past.
Geology of the Grand Canyon
Scientists think that the oldest rock layers found at the base of the canyon are around 1.8 billion years old; the oldest rock strata encompass parts of the Precambrian Era and the Paleozoic Era between 2 billion and 250 million years ago.
The Inner Gorge of the Grand Canyon boasts the oldest layer of rock in a place called the Vishnu Schist. Vishnu Basement Rocks is the name given to this rock set (a combination of metamorphic and igneous rock of a definite age found at this area). These rocks, which are predominantly schist (metamorphic) with granite (igneous), are around 1.7 billion years old, dating from an early period in Earth history known as the Proterozoic. Zoroaster granite is the name given to the intrusive igneous rocks found here.
The youngest rock is approximately 230 million years old located on the rim of the Grand Canyon in the Kaibab limestone sediment layer.
These rocks contain fossils like sea worm holes in addition to shells, other marine life, and younger human artifacts from early explorers and native tribes in the region. Scientists theorize that the Grand Canyon was once located partially or completely underwater, explaining the marine fossils as well as the water erosion that created the Grand Canyon as well as sediment layers like the Permian Coconino Sandstone which has ample sand dune deposits in it.
Biodiversity of the Grand Canyon
In addition to incredible geography, the Grand Canyon and the Colorado Plateau are home to many unique plants and animals including the bison, gray fox, bighorn sheep, and the Kaibab squirrel. 250 other species of birds reside in the park alongside 25 types of reptiles, 70 mammal species, and 5 species of amphibians.
There are five major ecosystems in the Grand Canyon:
The mixed conifer forest or boreal forest ecosystem occurs exclusively at the Grand Canyon’s highest elevation, between 8,200 and 9,200 feet on the North Rim. Deciduous trees, such as aspen, are common, as are evergreen trees, such as Douglas fir and Englemann spruce.
On both the South and North Rims, the Ponderosa Pine Forest is located at the Grand Canyon’s second highest elevation. This area receives an average of five feet of snow per year During the summer, the area is prone to violent thunder storms that result in flash floods. The Kaibab squirrel is endemic to the Ponderosa Pine Forest.
The Pinyon Juniper Woodland is found in sunny places below the North and South Rims that receive roughly half the rainfall of the Ponderosa Pine Forest. It is characterized by drought-resistant species such as Utah juniper and pinyon pine.
Desert Scrub is the warmest and most arid of the Grand Canyon’s five habitats. It is only found at extremely low elevations. Plants have adapted to an unpredictable and restricted water source by becoming smaller, with the exception of agave. Cacti, sage, yucca, and blackbrush are all found in abundance. Mammals such as bighorn sheep and mice are found here. The Desert Scrub habitat is home to the majority of the Grand Canyon’s reptiles, including the collared lizard.
Riparian ecosystems are the smallest of the Grand Canyon ecosystems and are located along the Colorado River’s banks near the Grand Canyon’s bottom. Because riparian ecosystems are defined by a continual presence of water, they are densely vegetated, containing cottonwood trees.
The Colorado River
Over the millennia the base level of the Colorado River changed as waters receded from the North American continent- as this water drained faster and eventually leveled off, differential erosion caused the stratification of the rock to become visible. Volcanic eruptions caused a layer of ash to form another rock stratum in the canyon which is now amongst the youngest rock studied (around 100,000 to 3 million years ago).
Recent findings suggest that the Colorado River began flowing through the ancient Grand Canyon approximately 17 million years ago.
The Colorado Plateau’s increase in elevation was uneven, however; the water in the Colorado River ran and eroded quicker, but the North and South Rims of the Grand Canyon settled with about 1,000 feet of elevation difference between them. Both rims receive a similar amount of rainfall during the year; the runoff from the North Rim flows towards the base of the canyon to the Colorado River which the runoff from the lower South Rim flows away from the canyon.
This means that the majority of the steeper, shorter canyons to form off the South Rim while longer canyons form near the North Rim and are more likely to have a tributary of the Colorado River flow through them close to year round.
The geologic significance of the Grand Canyon is still being recognized. As scientific dating and knowledge continues to increase new information about the origins of the canyon are being discovered. The preserved geological strata that is visible today still offers much to be studied; the intricate story of the North American continent being changed and shaped into the places we live today.
Anderson, C. A. (1951). Older Precambrian structure in Arizona. Geological Society of America Bulletin, 62(11), 1331-1346. https://doi.org/10.1130/0016-7606(1951)62[1331:OPSIA]2.0.CO;2
Grand Canyon Ecosystems. (n.d.). USGS.gov. https://www.usgs.gov/geology-and-ecology-of-national-parks/grand-canyon-ecosystems
Grand Canyon Geology. (n.d.). USGS.gov https://www.usgs.gov/geology-and-ecology-of-national-parks/grand-canyon-geology
Grand Canyon National Park. http://travel.nationalgeographic.com/travel/national-parks/grand-canyon-national-park/
Grand Canyon National Park: Animals. December 2013. http://www.nps.gov/grca/naturescience/animals.htm
Grand Canyon Facts and Figures. http://explorethecanyon.com/explore-learn/grand-canyon-facts/