The Grand Canyon is an overwhelmingly imposing chasm that seem to creep in the middle of the Arizona Desert. It is approximately 277 miles (446 kilometers) long, about 18 miles (29 kilometers) wide, and plunges to an average depth of 1 mile (1.61 kilometers). Visitors run out of superlatives to describe the magnificence of this Earth surface.
The striated walls of the Grand Canyon is made up of layer upon layer of ancient rock, whose blazing colors glisten with the frolicking of light. The deepest levels of the canyon’s walls are formed of dark-colored metamorphic rock called schist, which splits easily, and fossil-rich igneous rock known as granite.
The surface of the Kaibab Plateau was once the floor of an ancient ocean. Between 570 million and 248 million years ago, in the Palaeozoic Era, layers of shale (sedimentary rock formed from compacted clay and other minerals), limestone rocks and sandstone were deposited on the plateau’s surface. These rock deposits were laid down on top of an even more ancient layer of igneous rock (called Vishnu schist), which is estimated to have been formed about 1,700 million years ago, in the Proterozoic Era. Later, molten rock penetrated weak spots in the schist layer and cooled to form granite intrusions.
The descriptions of each of the next 9 levels (from lowest to uppermost) of the walls of Grand Canyon are provided below, with emphasis on the kinds of rock – how and when they were formed – that compose each level.
Tapeats Sandstone:
This level, which caps the Vishnu schist, is composed of clastic sedimentary rocks (specifically, sandstones), and is estimated to have been formed between 545 million and 525 million years ago by deposits swept by a new sea into the area. The rocks are dark brown in color, making this level distinct from the rest.
Bright Angel Shale:
Capping the Tapeats Sandstone is the Bright Angel Shale layer, which is made up of siltstone and shale. Its color varies, with green being the dominant shade. This level, which was formed from the hardened thick layers of fine sediments that began to cover the area as it grew deeper, is estimated to have been formed between 530 million and 515 million years ago, in the Cambrian Period.
Muav Limestone:
Estimated to be between 515 million and 505 million years old, this level of gray limestone rock, which rests on top of the Bright Angel Shale, is proof that the ancient ocean that covered the Grand Canyon region continued to deepen further during that period. The layer of limestone is uneven in the western and eastern walls of the canyon – that is, it is less thick in the latter.
Redwall Limestone:
Formed between 340 million and 335 million years ago, around the Late Devonian Period, this layer of dolomites and marine limestones stands out among the other levels of the canyon’s walls. Its prominence is mainly due to its precipice’s unbroken steepness, with height that ranges from 500 to 550 feet (152 to 168 meters). Iron oxide runoff from the upper layers gave this level its deep red color, hence its name.
Supai Formation:
Sandstone, sandy shale and limestone make up this level, which is estimated to have been formed between 315 million and 285 million years ago, in the Permian Period. The level’s topmost layer, called the Esplanade Sandstone, gives this level its tan color, while its red color is provided by the shale rock. The deposition of the three kinds of rock that compose the Supai Formation was caused by the reencroachment of the sea that appeared to have demised for a long period since the period of the formation of the Redwall Limestone.
Hermit Shale:
Forming slopes atop the Supai Formation is the Hermit Shale, which is estimated to have been formed between 280 million and 265 million years ago. The level is composed of deep red-colored shales. Interestingly, the Hermit Shale is non-existent in the eastern side of the Grand Canyon. The formation of this level was the result of a tidal flat deposition that occurred over a long period in the region.
Coconino Sandstone:
The Coconino Sandstone level of the Grand Canyon was formed between 275 million and 260 million years ago. With its thickness measured to be approximately 350 feet (107 meters), this level is made up of pure quartz sand, and is prominent for its pale yellow-brown color. Continuous erosion and the subsequent covering of the upper surface of the Hermit Shale with giant sand dunes caused the formation of the Coconino Sandstone.
Toroweap Formation:
The layers of the Toroweap Formation are composed of sandstone, limestone, and shale. This level was formed some 260 million years ago; its color ranges from pale yellow to gray. The deposition of the rock layers, and the eventual formation of this level, was caused by the changing near-shore marine environments.
Kaibab Limestone:
Sandy limestone mostly composes the Kaibab Limestone, with fossil seashells found throughout the level. Almost the entire rim of the Grand Canyon is formed with this 250 foot (76 meter)-high cliff. The color of this topmost level ranges from cream to off-white. Kaibab Limestone was formed about 250 million years ago, around the Late Triassic Period.
In a nutshell, the bands of rock that make up the bottom of the deep granite gorge of the Grand Canyon are schists from the Precambrian Period, while those in the upper part of the canyon walls are the different kinds of rock – as enumerated above – that date from the Palaeozoic Era.
