KAIBAB FORMATION   (270 million years old) 

The Kaibab Formation is a 350 foot thick light gray to tan colored cliff at the canyon rim. This layer of rock was named after the Kaibab Plateau. The formation is composed of sedimentary rocks like limestone, dolomite, and sandstone.  Thousands of years after the formation of this top layer, the Kaibab Plateau was raised by geological processes to its present altitude - which averages 7,000 feet at the south rim, and 8,200 feet on the north rim. This layer is very hard, and resistant to erosion.  This resistance to erosion is also shown by the sheer cliff faces in this layer.  When rocks are impermeable, they are most resistant to erosion, and they form steeper cliffsides.

TOROWEAP FORMATION (275 million years old)

The Toroweap Formation formed during the Permian Period, is 250 feet thick, and is home to a vegetated slope with a low cliff near its base. This layer is the layer of trees.  Although this layer is 80% limestone, it also has the most diverse rock collection with: sandstone, mudstone, redbeds, gypsum, limestone, and dolomite. There was once a body of water near this layer, and the salty water left sediments exposed to that water. The limestone cliff is called the Brady Canyon Member, and it represents the deepest water, as it contains various shellfish fossils. 

COCONINO SANDSTONE   (275 million years old)

The Coconino Sandstone layer formed during the Permian Period, is 350 feet thick, and is a light tan, nearly white, vertical cliff. The surface of Earth during the formation of the Coconino Layer was a Sahara-like sand sea, called an erg. An erg is a windblown dune desert, and it actually stretched from present day Arizona all the way to Canada. This layer is one of the most distinct layers because it has sand dune shapes at the top. This layer contains a lot of dune quartz.  To turn this kind of sediment into rock a natural glue is required; silica and calcite cements are most common. Oddly, there are many reptile and invertebrate tracks in the layer, but no fossilized bones. 

HERMIT FORMATION   (280 million years old) 

The Hermit Formation was formed during the Permian Period, is 300 feet thick, and contains a red slope below the white coconino cliff. This formation provides most of the red color the Grand Canyon is known for. This color comes from iron-oxide in the rock. Oftentimes, this layer is called the Hermit Shale, even though hermit in the layer is not actually shale (soft, finely stratified sedimentary rock that comes from mud or clay), but it is siltstone or mudstone mixed with fine grained sandstone. This layer contains animal tracks, mud cracks, and raindrop imprints. There are also large dragonfly impressions, and many types of worm burrows. Plant fossils like ferns and conifers were also found. These fossils and sediments show geologists that these animals lived in a semi-arid lowland where meandering rivers ran between forested banks. 

SUPAI GROUP   (285-315 million years old) 

The Supai Group formed during the Permian and Pennsylvanian Periods.  This layer is 1,250 feet thick, and composed of sandstone cliffs and shale slopes. The Supai group forms the iconic red stairsteps of the Grand Canyon. These steps are four formations composed of rust-red sandstone, siltstones, shales, and a few limestone beds. This layer formed in many different environments, but the most prevalent was a coastal desert with aeolian sands (cold and hot desert). The four groups (pictured at the left) in descending order are: 

• Esplanade Sandstone which is 300 feet thick and cliff forming

• Wescogame Formation which is 200 feet thick

• Mankacha Formation that is 300 feet thick

• Watahomigi Formation that is 150 feet thick

REDWALL FORMATION   (340 million years old)

The Redwall Formation formed during the Mississippian Period and is around 500 feet thick.  This layer consists of a very tall, vertical red cliff about halfway between the top and bottom of the canyon walls. The redwall layer is the chief cave-forming layer of the Canyon, with small to large entrances visible from any viewpoint on the rim. Ironically, redwall is not actually supposed to be red because it is made out of limestone, which would give it a gray color, but the iron rich layer above it (Supai) stains it red. The limestone it is composed of is made out of calcium carbonate shells of sea creatures. When marine animals die their shells fall apart in the waves and become the lime mud, which eventually forms limestone.  Animals that weren't broken up became enveloped in the surrounding mud, and became fossils.

TONTO GROUP   (500-520 million years) 

The Tonto Group is composed of the next three layers in this timeline.  The entire group was formed during the Cambrian period, is 1025 feet thick, and has pronounced yellowish ledges on top, the Tonto Platform in the middle, and a brown cliff below. This formation took millions of years to form and each layer had to complete before the next layer could begin forming, making them all different ages. The west side of the rocks are older than the east.

MUAV LIMESTONE   (505 million years old)

The top layer of the Tonto Group is the Muav Limestone Layer.  This layer is 375 feet thick, and contains the ledges and slopes below the Redwall cliff. The Muav Formation is a mottled, nodular, shaly, yellowish cliff in the lower part, a covered slope in the middle, and a ledgy cliff, often stained red in the upper part where it contacts the redwall. Fossils in this layer are trilobites and brachiopods. Also scattered in this layer are invertebrate tracks and trails. The eastern part of this layer is more of a shaly formation containing much terrigenous material, while on the west side, it is more pure marine limestone. 

BRIGHT ANGEL SHALE   (515 million years old)

The middle layer of the Tonto Group is the Bright Angel Shale Layer.  This layer is 325 feet thick, and forms a broad greenish slope. This layer consists mostly of green, shale mudstones. Most of the formation is a sediment-covered slope or platform broken up by low sandstone ledges. The fossils found in this layer include 47 species of trilobites, inarticulate brachiopods, and primitive mollusks. This layer is unique because shale has a thin-bedded nature.  The green color we see comes from the mineral glauconite. This mineral is known to only come from ocean sediments, which is another indicator of a marine environment.

TAPEATS SANDSTONE   (515 million years old) 

The last layer in the Tonto Group is the Tapeats Sandstone Layer.  It is about 300 feet thick and is identifiable by its distinct layers, its brown color, and its massive cliff.  Much of the sand in this layer is coarse-grained, and can be anywhere from pea sized grains to much larger. Some of the grains are beautifully colored, but not all, giving the sandstone its overall brown appearance. The base of this layer also contains a conglomerate member called the Hotauta Conglomerate.  This layer contains schist and granite pebbles. 

VISHNU COMPLEX   (1,700 million years old)

The oldest and lowest layer of rock in the Grand Canyon, the Vishnu Complex was formed billions of years ago during the Proterozoic Era.  This layer has an unknown thickness, because it hasn't been entirely cut through yet.  It is composed of a black rugged inner gorge, with pink and white granite plutons. This rock composition makes it incredibly difficult for the Colorado River to erode and downcut through, especially since the flow of the river through the canyon is now controlled by the Glen Canyon Dam.  This layer is not only the foundation for the whole Grand Canyon, it is also among the basement rocks for all of Arizona.