Park Passes. Technical Announcements. Employees in the News. Emergency Management. Survey Manual. The beginning of the story starts at the bottom of the canyon and moves forward in time as you get closer to the rim. Stratigraphy is the study of the rock layering, and reveals a wealth of information about what Earth was like when each layer formed.
In the Grand Canyon, there are clear horizontal layers of different rocks that provide information about where, when, and how they were deposited, long before the canyon was even carved. The Law of Superposition states that sediment is deposited in layers in a sequence, the oldest rocks are on the bottom and the youngest rocks are on the top, similar to the way that sand piles up in an hour glass.
This principle is a key part of determining the relative age of a rock layer. The three main rock layer sets in the Grand Canyon are grouped based on position and common composition and 1 Metamorphic basement rocks, 2 The Precambrian Grand Canyon Supergroup, and 3 Paleozoic strata. These three main sets of rocks were first described by the explorer and scientist John Wesley Powell during his expeditions of the Grand Canyon in the late s and early s.
Unconformities are gaps in the geologic record that occur when rocks or sediments are eroded away and time elapses before new deposition occurs. New sediment eventually forms new rock layers on top of the eroded surface, but there is a period of geologic time that is not represented.
Types of Rock. The three main types of rock are igneous, sedimentary and metamorphic. Igneous rocks are cooled magma melted rock found underground or lava molten rock found above ground. Granite cooled from magma, known as an intrusive igneous rock and basalt cooled from lava, known as an extrusive igneous rock are two types of igneous rocks.
Sedimentary rocks are formed by smaller pieces of sand and mud stick together in layers. Examples include: sandstone, mudstone ,shale , siltsone, chert, limestone, and more. Sedimentary rocks often contain fossils that can be used to help identify the age of the rock. Certain fossils, called index fossils, are particularly useful because they are abundant in a relatively narrow time range.
Over time, pressure increases as sediment increases, and minerals help form these rock layers. All three rock types can be found in the Grand Canyon, and each layer adds an important understanding to the geologic history of the region. The oldest rocks in the Grand Canyon, found at the bottom of the canyon, are primarily metamorphic, with igneous intrusions the name given to when magma or lava enters or cools on top of previously formed rock.
On site you will easily notice at least 3 layers : one of sandstone, one of dark schist and another of light limestone, which correspond respectively to previous deposits of sand, mud and calcified remains of marine organisms. The dominant color is red, which derives from the oxidized iron present in all the rocks.
On the rocks, there are also signs of strong volcanic activity, which has contributed significantly to the formation of the canyon. Throughout the Grand Canyon there are about one hundred conical mountains on which you can easily find calcified dark rock flows descending from the sides.
These phenomena are about , years old and can be easily observed from Toroweap Point , for example. The last eruption that caused lava to flow to the bottom of the canyon dates back , years ago and some geologists believe that there are still active volcanoes that are potentially dangerous. When the water finally receded from the area, an immense and vast plain was revealed that, due to the collisions of the plates, rose up to become a plateau.
At this point, the area was completely exposed, but there was still no trace of the Grand Canyon. While the beginning of the whole process sinks into a remote past, it seems that the origins of the Grand Canyon are relatively more recent. This data was deduced by dating some debris from the area with sophisticated instruments and it would imply that the canyon was dug at a rate of meters every million years 3 centimeters every century!
Does it look like it took that long? Obviously, there are multiple theories, including that of the Spill-Over Theory , developed in by geologist John Douglass.
According to the scholar, the Colorado River , continuing its course from the Rocky Mountains, had filled a basin known as Bidahoci Lake , transforming it into an immense lake now drained from which the river overflowed until it dug into the rock the first crack of what would become the Grand Canyon.
The speed of excavation and the depth of the gorge would be due to the slope of the river bed, witnessed by the numerous rapids, while the width of the gap is due to the numerous landslides caused by the weakening of the less resistant rock layers shale in contact with natural elements once weakened the rocks give way to the force of gravity and landslide.
The canyon measures over miles long, up to 18 miles wide and a mile deep, making it one of the biggest canyons in the world. This natural landmark formed about five to six million years as erosion from the Colorado River cut a deep channel through layers of rock.
The Grand Canyon contains some of the oldest exposed rock on Earth. These rock layers have given geologists the opportunity to study evolution through time. The oldest known rocks in the canyon, called the Vishnu Basement Rocks, can be found near the bottom of the Inner Gorge. The Vishnu rocks formed about 1. Archaeologists have discovered ruins and artifacts from inhabitants dating back nearly 12, years.
Prehistoric humans first settled in and around the canyon during the last Ice Age , when mammoths, giant sloths and other large mammals still roamed North America.
Large stone spear points provide evidence of early human occupation. Hundreds of small split-twig figurines made between and B. The figurines are shaped like deer and bighorn sheep. Anthropologists think that prehistoric hunters may have left the figurines in caves as part of a ritual to ensure a successful hunt. The Havasupai people now claim the Grand Canyon as their ancestral home.
According to tribal history, the Havasupai have lived in and around the canyon for more than years. Almost all of the Havasupai ancestral land was taken for use as public land with the creation of the Grand Canyon first as a reserve and later a national park.
In , the Havasupai regained a large portion of their land from the federal government after influential newspapers including the Wall Street Journal , Los Angeles Times and the San Francisco Chronicle took up their cause. The Havasupai today make most of their money from tourism. The cerulean pools and red rocks of Havasu Falls, located near a remote portion of Grand Canyon National Park, draw about 20, visitors each year.
Spanish explorers led by Hopi guides were the first Europeans to reach the Grand Canyon in the s. More than three hundred years passed before U. American geologist John Newberry served as a naturalist on the expedition, becoming the first known geologist to study the Grand Canyon. A decade later, John Wesley Powell, another U. The first pioneers began settling around the rim of the Grand Canyon in the s. They were prospectors looking to mine copper. Early settlers soon realized that tourism was more profitable than mining.
President Benjamin Harrison first granted federal protection to the Grand Canyon in as a forest reserve.
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