• The rocks exposed within the Grand Canyon, range from the fairly young Kaibab limestone, the cap rock on the rims of the canyon, which is about 270 million years old to the oldest rocks found in the inner gorge, which have been dated at 1840 million years. For comparison geologists currently set the age of the earth at 4550 million years.
• The rocks may be ancient, but the canyon is relatively young, carving having taken place during the last 5-6 million years.
• The canyon occurred due to the heat and pressure that built up due to 2 colliding tectonic plates, resulting in the Colorado Plateau being raised more than 3000 m.
• There is a difference in height of 1800 m from Point Imperial on the N Rim to the Colorado River, and the river is 850 m above sea level.
• Over the 446 km length the jagged Grand Canyon varies in width, from 13-26 km. This great width is not due to erosion by the Colorado, but from rock layers collapsing around the river and its tributaries. Softer weaker layers erode faster, undermining the harder, stronger layers above, which eventually collapse. The river carries the eroded material to the Gulf of Mexico, much of what is SW California and SW Arizona is covered with material eroded from the Grand Canyon.
• A cross section of the Canyon walls reveals 12 rock layers, that span from 270 million to 1840 million years ago, with the exception of the period 1200-1680 million years. This is known as the Unconformity, I spoke of previously. We were so privileged to travel ‘through time’, to see all the layers, on our trip down the Colorado.
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