The rock layers were created at the bottom of a vast
sea millions of years ago when sedimentary deposits
accumulated to a thickness of nearly a mile. Later, a
collision of tectonic plates raised the entire region
thousands of feet to form the great Colorado plateau
that now lies 7000 to 9000 feet (2100 to 2750 meters)
above sea level. The Colorado River slowly formed a
basin to carry away water from this region and over the
millennia it eroded down through the numerous
sedimentary layers. Eventually the river cut this
mile-deep channel that we have named the Grand Canyon.
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