Grand Canyon viewed from Hopi Point, on the south rim. New evidence suggests the western Grand Canyon was cut to within 70 percent of its current depth long before the Colorado River existed.
The age of the Grand Canyon is a puzzle, because the Colorado River has washed away many of the clues.
So for 150 years, geologists have pondered the processes shaping the canyon, one of the world's great wonders and a living laboratory for understanding Earth history.
The gorge's rugged beauty, with its sheer cliff and steep slopes, looks young. And the general scientific consensus, updated at a 2010 conference, holds that the copper-colored Colorado River carved the Grand Canyon beginning 5 million to 6 million years ago. Many strong lines of evidence support this theory, including a pile of gravel and limestone pancaked with lava at a place called Muddy Creek.
This geologic layer cake, at the western mouth of the canyon, locks down the Colorado River from exiting the canyon before 6 million years ago.
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