The Grand Canyon might be a popular destination for photographers, rafters, hikers and wildlife lovers, but it’s also one of the only places in the world where visitors can hold a chunk of rock that’s nearly 2 billion years old. Grand Canyon visitors get a unique view the Earth’s geology up close and as Norman MacLean so eloquently said experience the “the basement of time.”
Geology has always been a part of Grand Canyon National Parks history. Since 1858 geologists have been studying the canyon’s geology climbing into steep slot canyons, scouring it’s crumbling cliffs and floating the mighty Colorado River. Though scientists are still unsure of the canyon’s exact history, many scientists have pieced together a linier history that includes the Colorado Plateau, the mighty Colorado River and millions of years of erosion.
The Early Years
The Grand Canyon’s story begins nearly 2 billion years ago when Vishnu basement rocks were formed by intense heat and pressure. Though these rocks are visible down by the Colorado River, the canyon itself didn’t really start forming until approximately 70 million years ago. The Colorado Plateau, approximately 130,000 square miles of land located across four states within the Four Corners region, was pushed upwards at elevations of 10,000 feet. The upward movement drastically changed the drainage of the southwest desert. As water began to pour off the western slop of the Rocky Mountains, the Colorado River became a destructive force carrying rocks and silt that chipped away at the plateau’s soft surface. As the river cut deeper into the plateau’s surface the banks began to erode forming a small canyon.
Over millions of years the Colorado continued to drag debris from the Rocky Mountains and surrounding desert to the Pacific Ocean cutting the canyon deeper and deeper. Wind, rain, winter weather and the hot summer sun all played a key element in the canyon’s erosion as the years continued on.
Today the Grand Canyon is continuing to grow as the weather and Colorado River chip away at the canyon’s walls. Though the change is slow, over millions of years the canyon may expand even more.
Layers and Layers of Rock
When looking at the Grand Canyon it’s impossible to not notice the various colorful layers of rock visible across the canyon’s walls. One of the most interesting aspects of the Grand Canyon’s geology is the fact it’s comprised of 13 distinct groups of rock, which each highly visible. The layers in order from the newest to oldest are:
Kaibab Formation (270 million years)
Toroweap Formation (273 million years)
Coconino Sandstone (275 million years)
Hermit Formation (280 million years)
Suapi Group (315-285 million years)
Redwall Limestone (340 million years)
Temple Butte Formation (385 million years)
Muav Limestone (505 million years)
Bright Angle Shale (515 million years)
Tapaets Sandstone (525 million years)
Grand Canyon Supergroup (1.2 billion?740 million years)
Vishnu basement rocks (1.84-1.68 billion years)
Several of the canyon’s landmarks are named after these rock structures and hold special significance in the geological makeup of the canyon. One of the most interesting aspects of the Canyon is the fact that each of the rock layers erodes at a different pace. This is why some of the canyon’s walls are sheer cliffs, while others gradually slope down. The layers also appear a different color because the mineral content of the rock layers affects each layer. Since the canyon is always changing the rims are not stable features and it is not uncommon to hear of stories where visitors got too close to the edge of the canyon and fell down.
The Colorado River
When discussing the geology of the Grand Canyon it’s impossible to ignore the mighty Colorado River. Starting high up in Rocky Mountain National Park, the Colorado River flows over 1,400 miles across five states en route to the Pacific Ocean. The river is a key player in the Grand Canyon’s history and is also a driving force as the canyon continues to expand. Throughout the canyon the Colorado River meanders through long slow stretches and pounds through world-class rapids. The river is continuing to slowly cut down into the Grand Canyon and though there are now several dams along the river will continue to ever so slowly change the canyon’s profile.