The Grand Canyon is one of the rare places on Earth where you can see rocks that were deposited billions of years ago. Most rocks of this age have either been eroded away, or are buried deep within the Earth's crust. In this U.S. National Park, however, about 5–6 million years ago the Colorado River began to carve out a canyon that revealed a geologic history like no other.
The Rock Formations of the Grand Canyon
There are 13 rock formations that the Grand Canyon is made out of. The names of these rock formations and the Periods or Eras they were deposited are:
- The Vishnu Basement Rocks deposited during the Precambrian-Late Paleoproterozoic Era
- The Grand Canyon Supergroup deposited during the Precambrian-Mesoproterozoic to Neoproterozoic Era
- The Tapeats Sandstone deposited during the Early Cambrian Period
- The Bright Angel Formation deposited during the early to middle Cambrian period.
- The Muav Limestone deposited during the Middle Cambrian period
- The Temple Butte Formation deposited during the Paleozoic Era to the Middle to Late Devonian Period
- The Redwall Limestone deposited during the Paleozoic Era – Late Early to Middle Mississippian Period
- The Surprise Canyon Formation deposited during the Paleozoic Era – Late Mississippian Period
- The Supai Group deposited during during the Paleozoic Era – Early Pennsylvanian Period
- The Hermit Formation deposited during the Paleozoic Era – Early Permian Period
- The Coconino Sandstone deposited during the Paleozoic Era – Early Permian Period
- The Toroweap Formation deposited during the Paleozoic Era – Late Early Permian Period
- The Kaibab Formation deposited during the Paleozoic Era – Early Middle Permian Period
The Vishnu Basement rocks are metamorphic and igneous and are the oldest rocks in the canyon, estimated to be about 1.8 to 1.6 billion years old. The metamorphic rocks formed as a result of a collision between a series of volcanic islands and the North American continent. The igneous rocks are what is left of the volcanic islands.
Geologic Evidence of a Changing Landscape
The Grand Canyon Supergroup – deposited about 1200 to 740 million years ago – is a thick rock formation found only in the Grand Canyon and contains primarily sedimentary rocks, but also has igneous and metamorphic rocks. This formation was deposited in a great rift basin as tectonic activity pulled the North American Continent apart and subsequent rising sea levels transported sediment into the basin. Around 800 million years ago, after most of the rock was deposited, this formation was faulted and tilted as the North American continent continued to be pulled apart.
The remaining rock formations, representing deposition between 525 and 270 million years ago, were all deposited as sediments in fluvial or marine environments. These deposits tell a story of a dynamic landscape that changed many times over millions of years. For example, the Tapeats sandstone, deposited around 525 million years ago, shows evidence of an environment similar to that of a modern day river delta. The Redwall limestone was deposited in a shallow to deep sea environment – evidence of variations in sea level – about 340 million years ago. The Supai group was deposited about 315 to 285 million years ago in a coastal environment that was sometimes swampy while at other times dry and sandy.
Source:
National Park Service - Grand Canyon Geology
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Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
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