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From Koinonia House - June 15, 2011

The Grand Canyon is a geological wonder, a vast chasm stretching 277 miles west to east through northern Arizona. The canyon offers one of the best geological cross sections in the world, with nearly 30 distinct layers found from the bottom to the top; its mesas, buttes, colorful slopes and spires illustrate the geological story of the great American southwest. School children are fed a simple tale about how the canyon was formed, but as any honest geologist will admit, nobody knows exactly how it got there. 

The true cause of the Grand Canyon is still hotly debated among geologists, and all recognize there's no solid answer. There are too many missing pieces. The basic park ranger explanation is that the Colorado Plateau - 130,000 square miles covering northern Arizona, southern and eastern Utah, western Colorado and northwestern New Mexico - began to rise up 50-70 million years ago, causing the existing Colorado River to downcut. After millions of years of steady uplift, the Colorado River carved out the Grand Canyon. The higher the plateau rose, pushed upward by magma from deep in the earth, the more powerful the erosional forces of the river proved to be. 

The Colorado River was tamed a great deal when the Glen Canyon Dam was finished in 1966. The dam controls the flow of the river now. The Colorado's flashfloods once carried boulders the size of VW Buses, and it transported an estimated 160 million tons of sediment every year, scouring the canyon bottom. Still, many people consider the vast expanse of the Grand Canyon and despise the Colorado as an underfit river, one that could not have possibly hauled out all the necessary sediment. 

A Few Puzzles:
The simple explanation does have serious geological issues. The Colorado River flows into the Gulf of California – the Sea of Cortez - which contains sediments from geologically young Pliocene layers - not older layers.  It appears that the eastern part of the Grand Canyon is much older than the western part of the Grand Canyon, but nobody knows exactly what happened. 

The western end of the canyon is fairly young. Local sediments come from the Basin and Range area to the west of the Canyon and are from Miocene layers. No river could have carved through there until after the Miocene. There's also no evidence that an older Colorado River ran through the Grand Wash Cliffs at the western end of the canyon. There is therefore an upper Colorado River system to the east that did not originally continue west of the Colorado Plateau. 

Alternate Theories:
The first thought, of course, is that the deposits were carried away by a different route. Perhaps the canyon was carved by a river that flowed down through Marble Canyon through what is now the Little Colorado River, draining into the Rio Grande. According to the theory, another small but steep and vigorous river rushed westward across the Basin and Range. It moved eastward by headward erosion until it ran into the upper Colorado. It "captured" the Colorado , caveman style, and the two married and carved the Grand Canyon in 4-6 million years, dumping into the Sea of Cortez like today. 

There's a problem there, though. The Continental Divide would have prevented the Little Colorado River from reaching the Rio Grande, and the sediment evidence is not there. 

Some argue that the old river flowed south at Peach Springs Canyon, until the river burst through whatever blocked the way to the western part of the Grand Canyon. Some argue that the Colorado Plateau tipped one way and then the other as it rose so that the Colorado River flowed in the opposite direction. Some argue the river flowed underground, or flowed northwest, draining into lakes in Nevada and Utah. 

The deposits to prove these drainage systems haven't been found.  That's part of the problem; there is a lot of data that is just plain missing.