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The Grand Canyon is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile (6,000 feet / 1,800 metres). 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 there is debate among geologist just exactly how old the Grand Canyon is (either 6 or 16 million years old) it remains a testament to the unstoppable power of erosion.

The result of all this erosion is one of the most complete geologic columns on the planet, as seen below.

Click to enlarge

Although I’m not sure it’s the geology which attracts so many tourists, about five million visitors per year, it no doubt is one of the world’s greatest wonders.