Popular Science Monthly/Volume 69/November 1906/The Making of the Grand Canyon of the Colorado
|THE MAKING OF THE GRAND CAÑON OF THE COLORADO|
By Professor A. R. CROOK
CURATOR, ILLINOIS STATE MUSEUM OF NATURAL HISTORY
THE Grand Cañon of the Colorado furnishes the most impressive illustration of cañon-making forces to be found, and presents a fascinating chapter of world history.
Nearly every visitor to the Cañon attempts an explanation of the manner of its making, and their explanations may be broadly grouped under five types—the explanation of the Indians who for centuries have inhabited the Colorado River region, that of one of the oldest white settlers in Arizona, that of a successful Chicago business man, that of a famous literary man, and finally that of men who have studied various phases of world making long enough to have learned the chief principles involved.
The Indians who have lived in Arizona, generation after generation, might be expected to have some notion of the origin of the Cañon. Their explanation is that a wise chieftain long mourned the death of a beloved wife. Finally, in pity, one of the gods made a great cleft in the earth, took the chieftain to the Happy Hunting Ground to see his wife; and then upon their return, fearing that others might go that way, the god hurled a river in the cleft where it is now flowing, effectually barring the way against intruders. The 'god-made' theory of the Indians is unsatisfactory as the infant science of any race always is.
The explanation of one of the oldest settlers in the region is hardly better. It is that of the widely-known John Hance. One morning he entertained the writer with the picturesque stories which he has poured into the ears of many an amused traveler, telling how thirty years ago he went from the Atlantic coast to Arizona to find room for his energies. In the east he was crowded. In Arizona he found opportunity to expand. A few years ago he used to tell that he dug the cañon, but says that he no longer makes the statement, because a little girl asked him where he put the dirt! The man-made explanation of the white man is no more satisfactory than the god-made theory of the Indian.A Chicago business man who knows how to make dollars, thinks he knows how the cañon was made, and after visiting it said to the author: "I'll tell you how that cañon was made. Once there was a
Fig. 1. One Mile from the Cañon—Seemingly a Thousand.
Fig. 2. John Hance at Old Grand View Hotel.
gigantic volcano. It exploded with such fury that one side became the finest dust and the other toppled over and now forms the channel through which the river is flowing." Much nearer to the truth than any of these explanations is that of Joaquin Miller. He suggests that the cañon is due to an underground river which worked away like the Green River has done in Mammoth Cave. Finally the roof fell in and behold the Grand Cañon. A picturesque explanation is Miller's and better than any of the others. Its truth consists in representing the river as the active agent, its error in the underground idea.
The geologist knows that the Colorado River cut out the whole cañon and regards the region as the finest example of river work on a grand scale in the world and as the type of all that is gigantic in displacement and denudation. The manner in which the river accomplished its tremendous task can be more easily comprehended by considering a number of facts; first, such as relate to the geography of the region; second, to its topography; third, to its stratigraphy and petrology; fourth, to its denudation and displacements. These different groups are closely interwoven with each other and the facts marshaled in one group are dependent upon those in all of the other groups.
Many tourists returning from the state of Colorado report that they have visited the Grand Cañon of the Colorado when they have simply seen the cañon of the Arkansas River—a cañon which would be a mere scratch in the side of the Grand Cañon. To see the chief cañon in the world they should have journeyed several hundred miles farther towards the southwest, to the region where a cañon 200 miles long has cut off the northwest corner of Arizona from the remainder of that state. Most tourists will now make their visit at the point called Grand Cañon Post Office, while the more fortunate ones will go east to Grand View and west to Cataract Creek. The railroad from the main line has been built to a well-chosen point where the cañon is a dozen miles wide and where for fifty miles to the east and west it is most gigantic and impressive. Within this region it displays all the salient points in its topography, succession of geological formations, different kinds of rocks, and erosion and sculpturing. So that one inquiring about the origin of the cañon can obtain all the factors to the answer in this locality.
Thanks to the good topographic map which the government has issued, one does not have to guess at the distances and depths in the region. One may refer to the map and not be disappointed. Accurate measurements do not rob the depths and distances of their magnificence, nor is exaggeration there necessary for impressiveness.The new survey shows that the elevation of the plateau through which the river has carved its path is between seven and eight thousand feet above sea level. At the head of the cañon the elevation of the river is twenty-five hundred feet, and by the time it has flowed two hundred miles to the end of the cañon it is only a thousand feet
above sea level. The distance between the top walls is from three to fifteen miles, and does not accord with the reports and pictures of the early government expeditions to the region. From El Tovar Hotel and the Grand View one sees the cañon at its broadest stretch, where for more than fifty miles it is a dozen miles wide and is filled with buttresses and buttes, towering from two to five thousand feet above the river.
The rim of the northern wall presents a nearly horizontal line. But a bird's-eye view from the western end of the canon would show the country to the east to be divided into four plateaus, each dipping like cakes of ice in a river till met by its neighbor. The plateau north of the visitor at El Tovar Hotel is one of the blocks that has been raised highest and consequently has brought up the lowest rocks and exposed them to the corroding action of the river.
If with a high buzz-saw we could cut through the country from east to west for three hundred miles and could move out the section nearest us, we should see that the face of the cut opposite is composed of a, series of blocks higher towards the west and slipping down towards the east. What we are unable to do in this regard has in a manner been done for us, since for ages the Colorado River has been eating away and has exposed the outlines of the blocks and the various geological formations so plainly that they are easily distinguished.
Seated on the rim in some favorable spot, one sees the different formations spread out as clearly as if diagrammed in a text-book on geology. The Kaibab plateau, just to the north shows six or seven formations belonging to the four great rock systems. At the top is the bluish limestone which weathers into fantastic buttresses and pinnacles, many of them so dizzily perched as to give a constant challenge to the winds or to man to topple them from their precarious position and hurl them a thousand feet below. My companion could hardly find time to sleep, so great was his delight in prying off great blocks of stone and listening to their terrible crunch and roar as they fell hundreds of feet, striking a ledge here and there and finally crushed to powder, or, still in gigantic mass, they rested a thousand or more feet below. This top formation, which Powell called the 'Fortification limestone' is the 'Upper Aubrey' limestone. It is about five hundred feet thick.
Next below it, can be seen the great white four hundred feet wide band of Upper Aubrey sandstone which stretches like a ribbon in sight for fifty miles and more to the east and west. Its walls are even more precipitous than those of the Aubrey limestone.
Below it are a thousand feet of shelving red sandstone which form the 'Lower Aubrey.' These three formations—the Upper Aubrey limestone and sandstone, and the Lower Aubrey sandstone—constitute the Upper Carboniferous system which is so familiar to the inhabitants of the Mississippi Valley states as the source of coal, but which in this region is not coal bearing.
Following the Upper Carboniferous a shelf of shales leads out to the precipitous wall of the great 'Red Wall' limestone, which, with
its six hundred feet of deep red cliffs, presents one of the most striking members of the landscape. The Red Wall constitutes the Lower Carboniferous of the region.
Then there is a terrace—'The Esplanade'—often several miles in width, composed of green shales and sandstones. It is the 'Upper Tonto' formation. It leads by gentle slopes to the brink of another precipice, which is formed by the quartzites and hard sandstones of the 'Lower Tonto.' The Upper and Lower Tonto are the local names of the formation composing the system known the world over as the Cambrian. Together they are about seven hundred feet thick. The Lower Tonto forms the capping of the inner canon in the Bright Angel region.
Below it are jagged, twisted, dark-colored metamorphic rocks, which represent the Archæan—the oldest system of rocks in the world. Tourists call these rocks 'granite,' but they are schists and gneisses. They are in layers and have been subjected to extensive folding. The river has cut through the Archæan rocks to a depth of over a thousand feet and produced walls so precipitous that in most places a sure-footed prospector could not cling to them. Between them the river runs with the greatest speed and fury.
The visitor may see all these formations from the upper rim, but as he descends to the river and passes them in succession, he obtains a clearer idea of their relations and characteristics. They are clearly differentiated by constitution, structure and color. A study of these various strata makes it evident that the topography of the country is largely due to the difference in the kinds of rocks which the river encounters in its journey from the mountains to the sea.
Leaving the immediate vicinity of the cañon and going to the north, the tourist would come upon various younger geological formations which at one time buried the whole region. Although from ten to fifteen thousand feet thick, they no longer remain in the vicinity of the canon, having been washed away by flowing water after the elevation of the land in early Eocene times. When that was accomplished and the country for miles around was comparatively level, the land was again gradually raised and the river began in Neocene times to cut the outer cañon. When it had cut down to the Tonto terrace—' The
Esplanades'—elevation ceased and the river wandered back and forth in a lazy manner, widening instead of deepening its channel. Since in that arid region there was not enough rainfall to wash down the side walls, they have remained precipitous, while the main stream has had time to push them back until they are a dozen miles apart. Then, in the Pliocene, slow elevation of the plateau began again, causing the river to run swiftly and renew its carving. This action is proceeding at the present time with the result of deepening the inner cañon.
Standing on the cañon's rim and looking down upon the immense gulf, one marvels that so small a river could have accomplished so gigantic a work. But if he laboriously descends to the brink of the roaring river below and puts his hand into the rushing water and feels its burden of sharp sand driven along with great force, he obtains some conception of the efficiency of the tool. Quartz sand is harder than any of the common minerals in the rocks. Hurled by the rushing water against the sides and bed of the river, it cuts out a path through the rocks as a file does through soft iron.
Volcanic explosions had nothing to do with the making of the canon. If they had, there would be volcanic rock over all the region instead of in isolated patches, and all the topographic forms would be different. The canon is not the result of cracking apart of the earth's crust. If it were, the rock layers would dip away from the cañon; opposite sides would not match; they would lack marks of cutting parallel to the
bedding; their configuration would be independent of alternating hard and soft layers. The extensive cracking and faulting which does exist has been at right angles to the canon and has presented different kinds of rocks for the river to work upon, thus producing variously shaped walls. As the river carves into succeeding strata the crust is weakened and various buttresses sink towards the river.
Thus all signs lead to the conclusion that fire did not make the canon, nor did wind, nor earthquake, but that it was made by the same agent which in an hour carves tiny channels in a garden after a rain storm. That agent was running water, the water of the Colorado as for unnumbered years it has been flowing from snowy Rocky Mountain ridges to the hot sands which border the Gulf of California.