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Where is the Grand Canyon and What's the Big Deal?

Most of you probably visited the Grand Canyon at one time or another (or at least "should" have), one of the seven natural wonders of the world and all that.  Besides, its not  too far of a drive from Phoenix, AZ.  Grand Canyon occupies a large portion of northern Arizona and extends about 270 miles from Lees Ferry (just southwest of Lake Powell) to the Grand Wash Cliffs (just east of Lake Mead)--the longest canyon in the world.  "Only" a mile a deep, Grand Canyon is not the deepest in the world.  For example, the Washington's Colombia River Gorge measures over a mile and a half in depth.  Though not the deepest, Grand Canyon remains an incredibly impressive natural landform.  The Colorado River in the canyon's depths flows from the Rocky Mountains with tributaries supplying water from the Wind River Mountains and Utah Highlands.

Figure 1.  An image from space showing the Grand Canyon where snow covers the Kaibab Plateau, the mountain cut by the Colorado River to form Grand Canyon.

So what's the big deal?  Canyons are all over the place, and some are as big or bigger than the Grand Canyon.   Copper Canyon in northern Mexico represents a nearby example.  So why all the fuss over the formation of the Grand Canyon (there is a big fuss in case you didn't know), when canyons themselves happen all the time and all over the place.  Well, Grand Canyon qualifies as a "transverse drainage".  A transverse drainage flows through, via a canyon, what would be a topographic obstruction.  Take a look at the eastern portion of Grand Canyon in the upper and lower images.  The Grand Canyon cuts across the southern flank of the big white and dark green highland termed the Kaibab Plateau (a flat topped highland).  We've all known since childhood that water flows down hill.  So here's the big question with the Grand Canyon, "How did the Colorado River ever get across the Kaibab Plateau to carve the Grand Canyon?".  

Figure 2. An image from space that provides a close up of the Kaibab Plateau (white and dark green).  The dark green region comes from Ponderosa forests that inhabit the Kaibab Plateau and the white is snow.  Note that the Colorado River cuts across the southern end of the Kaibab Plateau via the Grand Canyon, hence the Grand Canyon represents a "transverse drainage"..  

Over thirty publications proposed, support, or combine hypotheses to explain Grand Canyon's developmental history.  And just so you know, Grand Canyon is not the only transverse drainage, they're actually quite common.  Transverse drainages provide a glimpse into the past, because we know the present landscape can not explain the present configuration of a drainage flowing across a mountain, hill, highland, or plateau.  If we deduce the mechanism responsible for a transverse drainage, then we have a snapshot of a past landscape that generated future mountain crossing rivers.  With this information, we can produce much richer landscape developmental histories and broaden our understanding  of possible alterations to the planet's current landscapes.  Let's see what we dig up about the landscape responsible for the Grand Canyon.

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