grand canyon

The Grand Canyon is a steep-sided gorge carved by the Colorado River in the United States in the state of Arizona .It is largely contained within the Grand Canyon National Park , one of the first national parks in the United States . The canyon is 277 miles (446 km) long, ranges in width from 4 to 18 miles (6.4 to 29 km) and attains a depth of over a mile (1.83 km) (6000 feet). . Nearly two billion years of the Earth 's geological history have been exposed as the Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted . While the specific geologic processes and timing that formed the Grand Canyon is the subject of debate by geologists, recent evidence suggests the Colorado River established its course through the canyon at least 17 million years ago. Since that time, the Colorado River continued to erode and form the canyon to the point we see it as today. The Colorado River basin (of which the Grand Canyon is a part) has developed in the past 40 million years. A recent study places the origins of the canyon beginning some 17 million years ago. Previous estimates had placed the age of the canyon at 5 to 6 million years. http://en.wikipedia.org/wiki/Grand_Canyon

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