The Grand Canyon's greatest significance lies in the geologic record that is so beautifully preserved and exposed in its walls.
What is unique about the canyon's geology is the great variety of rocks present, the clarity with which they're exposed, and the complex geologic story they tell.
There are really two separate geologic stories at Grand Canyon. The older story is the one revealed in the thick sequence of rocks exposed in the walls of the canyon.
These rocks provide an amazing (but incomplete) record of the Paleozoic Era (550-250 million years ago), and scattered remnants of Precambrian rocks as old as 2 billion years. The story these rocks tell is far older than the canyon itself (which only formed five to six million years ago), a relative youngster in geologic terms.
The second geologic story at Grand Canyon revolves around its origins: when and how did it come to be?
On one level the answer is simple: the Canyon is an erosional feature that owes its existence to the Colorado River (which is responsible for the depth of the canyon). Of equal importance are the forces of erosion that have shaped it and continue to shape it today - mainly running water from rain, snowmelt and tributary streams which enter the canyon throughout its length.
The climate at Grand Canyon is classified as semi-arid (the South Rim receives 15 inches/38 cm of precipitation each year; only eight inches/20 cm annually reaches the bottom).
When it does rain, it is usually in the form of sudden, violent storms, particularly in late summer. The power of erosion is therefore more evident here than in places which receive more rain.
Why does it look the way it does?
Grand Canyon owes its distinctive shape to the fact that different rock layers in the canyon walls each respond to erosion in different ways: some form slopes, some form cliffs, some erode more quickly than others.
The vivid colors of many of these layers are due mainly to small amounts of various minerals, most containing iron, which impart subtle shades of red, yellow or green to the canyon walls and corridors.
What is unique about the canyon's geology is the great variety of rocks present, the clarity with which they're exposed, and the complex geologic story they tell.
There are really two separate geologic stories at Grand Canyon. The older story is the one revealed in the thick sequence of rocks exposed in the walls of the canyon.
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These rocks provide an amazing (but incomplete) record of the Paleozoic Era (550-250 million years ago), and scattered remnants of Precambrian rocks as old as 2 billion years. The story these rocks tell is far older than the canyon itself (which only formed five to six million years ago), a relative youngster in geologic terms.
The second geologic story at Grand Canyon revolves around its origins: when and how did it come to be?
On one level the answer is simple: the Canyon is an erosional feature that owes its existence to the Colorado River (which is responsible for the depth of the canyon). Of equal importance are the forces of erosion that have shaped it and continue to shape it today - mainly running water from rain, snowmelt and tributary streams which enter the canyon throughout its length.
The climate at Grand Canyon is classified as semi-arid (the South Rim receives 15 inches/38 cm of precipitation each year; only eight inches/20 cm annually reaches the bottom).
When it does rain, it is usually in the form of sudden, violent storms, particularly in late summer. The power of erosion is therefore more evident here than in places which receive more rain.
Why does it look the way it does?
Grand Canyon owes its distinctive shape to the fact that different rock layers in the canyon walls each respond to erosion in different ways: some form slopes, some form cliffs, some erode more quickly than others.
The vivid colors of many of these layers are due mainly to small amounts of various minerals, most containing iron, which impart subtle shades of red, yellow or green to the canyon walls and corridors.
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