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Weathering prepares the material for transportation and transportation leads to corrasion.

Nowhere else on the face of the globe is one so vividly impressed by the vastness of the work of corrasion as in the northwestern part of Arizona.

These broad canyons, or canyon valleys, are carved by the streams in obedience to an interesting law of corrasion.

Where rocks take a polish, as in Marble Canyon, the scouring and polishing work of corrasion is seen in the shining bright surface as far as the water rises.

Weathering, wash, and lateral corrasion of the stream continue to widen the valley after it has reached baselevel.