It is difficult to comprehend the immensity of the yawning chasm that is the Grand Canyon.This sprawling gash in the surface of the Earth, in the middle of the Arizona Desert, is some 320 miles long and plunges at its deepest point-Granite Gorge-to a depth of 1 miles. At tis widest it is 18 miles across, and beneath Toroweap Overlook on the North Rim it measures just under 0.5 mile.
Around 60 milllion years ago in this region, the wide expense of the Kaibab Plateau separated two waterways, the Ancestral Colorado River to the east and a river system called the Hualapai cut back into the plateau in a process known as headward erosion. The daily eroding millions of tons of rock and earth along its course.
The surface of the plateau, once the floor of an ancient ocean, was the uppermost of many layers of sandstone, shale and limestone rocks deposited between 600 million and 250 million years ago in the Palaeozoic era.
While the river cut downwards, other erosive forces began on work on the rock faces it had exposed, splitting their surface. Extremes of heat and cold caused the cracks to widen; winter storms and spring snowmelts loosened a steady stream of sandy gravel and debris and bulldozed them through the stone channels. Gradually meeting less resistance, the river battered the earth with increasing force, tearing away the base of the valley as the rocks continued to bulge upwards, causing the walls through which it flowed to mount higher and higher.
More than 300 years later, in 1885, Lieutenant Joseph Christmas Ives, leader of an exploratory expedition in north Arizona, steamed up the Colorado River from its mouth on the Gulf of California for two hot mouths.Finally the waters became so treacherous the he decided to leave the ship and lead his soldiers overland. On the South Rim of what he called the Big Canon of the Colorado, Ives rode a mule along a ledge that was within three inches of the brinl of a sheer gulf 300 meters deep; while on the other side, nearly touching my knee, was an almost vertical wall rising to an enormous altitude.
Today the Grand Canyon is regarded as one of the most astounding vistas in North America and, like US President Theodore Roosevelt, many consider it "the one great sight which every American should see"
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