Geology of the Grand Canyon

An Open Book of Geologic History

They say that a trek through the Grand Canyon is a journey back into the past. A deep exploration of the Grand Canyon will reveal an almost unimaginably long history, readable in the layers of ancient rock, imbedded fossils, and geological formations. The history of the Grand Canyon goes back 17 million centuries, or 1.7 billion years. If you looked at a cross section of the Canyon, you would see layers under the basalt starting with the Late Cenozoic, down further to the Paleozoic, and finall the PreCambrian at the level of the Colorado River and Vishnu Group. The Grand Canyon is a fortunate opening in the otherwise-closed book of geologica history of the earth. If it weren't for the deep canyon, the layers upon layers of earth would not be exposed to us. Earth-shattering events such as the birth of the Pacific Ocean, the collision between North America and Africa, the formation of deserts, seas, and mountains are evidenced in the earth of the Grand Canyon. Also buried in the rock here are fossil remains of creatures we've never seen alive today, dinosaurs.

The Colorado Plateau

The Grand Canyon sits on a part of the earth that is relatively stable, so preservation of history is very intact here, unlike land to the West of the Grand Canyon, which has been shattered, broken and jumbled. Land to the east of the Grand Canyon, the Rocky Mountains, is also shattered and broken up, but by volcanic eruptions and erosion have scarred the deep layers of history, scrambling the historical evidence forever. That's why it's lucky hwe have the Grand Canyon to tell us about the geolocial history of this part of the planet. The relatively stable piece of earth on which the Grand Canyon sits is called the Colorado Plateau. It's unusual, but not unique, for having its flat layers exposed bove the earth in great striations, so high above sea level. The Grand Canyon is located on the western edge of the Colorado Plateau, abutting the Great Basin. As mentioned before, the Great Basin is characterized by a shattered, broken up foundation of rock. Therefore, the western side of the Grand Canyon, which is closer to the Great Basin, has more faults than the eastern end of the Grand Canyon.

Floating Continents

Two billion years ago, the earth's continents were nothing like they are today. They had different shapes, they were in different places, and they were totally unrecognizable from what they are now. The continents drifted, and still do, on the Earth's core, which is semi-liquid. They are very very old. Older than the sea floor. On the other hand the sea floor moves the itself along, continuously renewing the material, pushing the old material back down in trenches in the earth. This is how the sea floor is always fresh and relatively new, 200 million years or less. The continents are not continuously renewed like the sea floor. They are lighter, and they "float" higher up. They are old and battered, and billions of years old.

The Vishnu Schist

The piece of floating continent which would someday hold the Grand Canyon once containted a shallow sea through which occasionally would experience lava flows. If you look at the Vishnu Schist, you will see the type of schist that belies evidence of lava flows, which make up more than have of the famous schist. Schist is made when sediment is crunched, sometimes a result of collision between two large masses of land. That's what happened in this case. A land mass the size of California collided with what was the sea bed and pushed up the Vishnu Schist. It's comprised of shards of Zoroaster Granite, which is pink. The rest of the Vishnu Schist is black, so the visual effect is stunning and beautiful. This creation of the Vishnu Schist happened 1.7 billion years ago, according to radioactive dating.

Mountain Building

After the creation of the Vishnu Shift, skip ahead to just 830 million years ago, and during that time there is much uplifting of the earth, creation of mountains, and tilting of the land masses. The more mountains, the faster came the erosion, which flattened out the earth again, in what was to become the Grand Canyon area. The worn-down mountains are made of Shinumo Quartzite. Millions and millions of years of uplifting of the surface, then erosion erosion erosion, repeating the cycles over and over again, creating the layers and layers which are now exposed in the walls of the Grand Canyon.

The Paleozoic Era

The earth did not move for a long time, during the Paleozoic Era. There were no uplifting of large pieces of land, no schist formation. There was just the sea, coming in and going out, over and over again. Our continent was located down near the equator during this time, and the climate was tropical, millions of years ago. Remember, the continents float. The area that would become the Grand Canyon was on the side of the continent that faced the back. In other words, as the continent drifted, the Grand Canyon area was towards the back. Therefore, it didn't see much going on in the way of geological events. It wasn't on the forefront of movement and activity. It was just a coastal shelf, experiencing tides and erosion. The sea left deposits of limestone from shells, and mud from eroded mountains. Some of what was deposited was Tapeats Sandstone. More and more beach was created, as the sea encroached further and further each year. This happened for about 250 million years.

After millions of years of erosion and beach formation with layers of sandstone and siltstone piling up, the North American Continent collides with Africa and the Rockies and Appalachians were formed. Sand, silt, and mud from these new mountain ranges gets carried down, eroded, into the Grand Canyon area. New layers are formed, of different types of siltstone. Now winds came up and dried out the sediment, creating huge deserts. The old shale is now covered with sand, and the Coconino Sanstone layers were formed. Then the land "sunk" again and the sea ran over the deserts, starting the cycles of ebb and flow of the water, creation of beaches, creating the Toroweap Formation. It containted limestone, siltstone, and fossils from the sea.

At the end of the Paleozoic Era, the North American continent changes course in its drift and begins to move westward. Now our pre-Grand Canyon edge was no longer the trailing edge, but the forefront of the movement. Now they see lots of activity again. The land mass hits shoals which push up the Grand-Canyon leading edge of the continent, and builds mountains. Now we're in the Mezozoic Era. This, by the way, is the era of the dinosaurs.

The Colorado River

Through the Mezozoic Era there continues to be more and more building up of layers of sediment and sandstone until the area is too high for any ocean to ever cross again. It's now ready for the mighty Colorado River to tumble through the area and cut away the Grand Canyon to form what we know today as one of the natural wonders of the world.