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The Grand Canyon was formed by a combination of the uplifting
of the Colorado Plateau, and the Colorado River cutting
almost one mile through the plateau. In the course of its
277 miles (446km), the Colorado River drops 2000 feet. Rather than
being gradual, the river profile is like a staircase. Most
of the drops occur at about 160 rapids. The rapids are generally
formed by debris and boulders transported during floods from the many
side canyons. Those debris constrict the flow,
increasing the water speed. Some of the Grand Canyon
rapids reach class V, on the International
Scale of River Difficulty I-VI, with VI meaning
“unrunnable” – if a rapid is repeatdely
run that was once thought to be class VI, it is typically
reclassified as Class V. Unkar Rapids, considered
moderate in difficulty, are remarkable for the setting, on
a wide bend surrounded by undulationg badlands
in the most open part of the Grand Canyon.
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