Grand Canyon - Canyon Carving
( Originally Published Early 1900's )
THE great size of the Canyon has given rise to many odd theories regarding its origin. It is difficult to convince people that anything so huge could result from ordinary causes. They insist that the extraordinary, the accidental, the cataclysmic have been at work here. And, of course, spirits of the earth and air have played their part. The supernatural is usually invoked when the natural is uncomprehended.
Very likely when Cardenas and his company of men came across the deserts and paused abruptly here on the Canyon's edge, they thought it the end of the earth, or at least a volcanic chasm that rent the earth in twain. It was just the kind of place to harbor a Satanic contingent, and probably the Spanish imagination peopled it with demons. And to-day there are some spooky beliefs entertained about it. The hotel guides shake their heads and talk about suction winds that draw down into the f depths; of eagles and buzzards that never fly across the River, though they swing around under the walls; of Phantom Creek and Haunted Canyon across from El Tovar; of caves that moan and ghosts that groan, and lights that flicker at night. There is a bagful of queer stories for those that like them.
The aboriginal tale usually heard relates that a great chief who was inconsolable over the loss of his wife was taken to see her in the Happy Hunting-Grounds by the god Tah-vwoats. The trail thither was down the Canyon of the Colorado—made by the god for the purpose. He afterward brought the chief back to earth, and fearful lest others might travel the same Canyon trail, he turned a roaring river into it to make the way impassable. When Powell came down the Canyon in 1869 the Indians still believed the tale—believed that the River disappeared in the earth and that no boat could pass the rapids and whirlpools set in motion by Tah-vwoats.
There is a white man's tale, attributed to Joaquin Miller, that seems to run on all fours with the Indian legend, and was probably taken from it. It is in substance that the Colorado once flowed under-ground, perhaps for many centuries; that it was a lost river and, after disappearing, never rose again to the light of day; that canoes going down it never returned, but were dashed to pieces over subterranean waterfalls, the musical sounds of which were occasionally heard through the rock strata. Miller was perhaps not responsible for more than the theory that the River had run underground for an indefinite period and that finally the rock-roof had fallen in and exposed the Canyon. The fancy lends itself to poetry, but there never was any necessity for it as explanation.
Still another theory is put forth that suggests the great trench was originally an enormous crack formed by an earthquake, or by contraction of the cooled earth-crust, or by subsidence; and that the River, taking the line of least resistance, followed the crack and deepened its bed to the present proportions. But if the great trench had been produced by subsidence or volcanic action, the sedimentary layers of rock in the walls would have been dislocated and twisted where they now lie even and match each other perfectly across arenas and across the Canyon itself. The walls and buttes and canyons would have been different one from another in form; and volcanic rock, perhaps cinder cones, craters, and lava streams would have been apparent. No; neither subsidence nor contraction nor volcanism offers a way out.
Nor does the theory of one of the Canyon's oldest inhabitants,* that the River basin was the result of an anticlinal fold of the rock strata, that the break occurred at the point of the sharpest fold, and that the River eventually widened the break, help us much. Again, some large indication of the fold would be apparent in the existing strata if such a thrust had ever taken place over a wide area. The theory is more or less scientific, but neither the fold nor the theory seems to hold water.
None of these explanations is so acceptable to the laity as the one that supposes the whole width of the Canyon to have been filled at one time with a rushing river—a river a dozen miles wide and a mile deep. The most mentally dense can comprehend that the great Canyon could be carved out by water, provided there was enough of it. And, of course, nothing but a deluge could do the carving here shown.
But there is no more basis, in fact, to the wide-river theory than to the Indian legend. A river twelve miles across would argue greater rainfall than ever came to earth in geological times. Had there been such a rainfall, all the river-valleys of North America would show enormous widths; and the Colorado to furnish forth that flood would re-quire tributaries many times greater than now appear. The immense body of water could never have flowed through the narrower canyons lying to the northeast, such as the Marble or the Glen Canyon. Moreover, so vast a river would run swifter and cut deeper in the narrow places than in the wide places; the Marble Canyon would have turned into a mighty cataract and the Grand Canyon into an expanded lake. But there is no evidence that such a condition ever existed. Again, the theory is not necessary to an understanding.
The Colorado in all probability was never much wider or deeper than it now appears—that is, two, three, or four hundred feet across and with a depth of from perhaps ten to fifty feet . It never cut more than its own width. At no time in its history did its sand-hued waters wash the bases of the present Red Wall or creep up to the foot of the El Tovar cliffs whence you are looking down. It was always at the bottom of an inner canyon hewn by its own cutting, just as today. The ripsaw gash in the rock was made by the River it-self and not by an earthquake or an anticlinal fold. The cutting power of the River is here extraordinary, and yet easily explained by the inclination of its bed and the volume of its stream.
A river in its course to the sea carries with it various substances and materials. The floating pumice, wood, or other debris carried on the surface has little effect upon the river's bed or banks and may be dismissed from present consideration. The silts and sediments carried in the water, in solution and otherwise, have a decided grinding and wearing power, and, with great velocity, they in time cut out formidable circles, pockets, and channels, besides making deposits of mud, sand, and gravel upon banks and bars. The greatest wear, however, in a rapid stream comes from the sands, gravels, and boulders carried in the bed, churned along the bottom, and rasped about the encompassing walls. These form not only a sand-blast under water but a battering-ram that breaks through and wears down the stoutest rock—even the Archaean rock through which the Colorado at El Tovar is now running.
The swiftness of a stream is, of course, dependent upon the slope of its bed, and the degree of swiftness (with the volume of the water) sets the pace for the boulders that are moved. A river running three inches per second will carry with it fine clay, six inches per second will shift coarse sand, twelve inches per second is sufficient to move pebbles a half-inch in diameter, and six feet per second means that stones nine inches in diameter can be rolled and pushed down the stream-bed. The moving power varies as the sixth power of the velocity. A stream swift enough to roll a one-pound stone has merely to be doubled in swiftness to roll a sixty-four-pound stone. The stream that will carry the nine-inch stone has a velocity of six feet per second, or about two and one-half miles per hour. But the Colorado at the foot of Hermit Trail has a velocity ten times as great, or, say, twenty miles an hour !
The abrupt descent of the river-bed in the Grand Canyon is very pronounced almost everywhere. From the mouth of the Little Colorado to the Grand Wash, a distance of two hundred and eighteen miles, the fall is one thousand six hundred and forty feet. That means a descent of about seven and one-half feet per mile. Of course this is not uniform every-where. In some flat stretches it is less, and over rapids and falls it is more. In the Kaibab division of the Grand Canyon the average fall is something like twenty-one feet per mile. At one place above Grand View the descent is one hundred and thirty feet in three-quarters of a mile, and the waves on the rapids there are said to be something like thirty feet in height. In such places the lifting and rolling power of the River is enormous. With its velocity it can hurl along boulders weighing tons and crush the hardest stone to powder. The striking, breaking, grinding power of these boulders, especially in flood-times, is, indeed, difficult to overestimate. When you are down at the River take up some of the sand that you will see pocketed along the shore and you will find it almost as fine as flour. Notice, too, the boulders in the stream, how they are rasped and rounded. They are being reduced to sand.
The River is a terrific grinding-mill—a mill that never stops.
Now the most pronounced wear upon a stream-bed such as this is vertical—that is, down in the channel. The bed if seen in a cross-section would resemble a V. The River is cutting down through the dark rock day in and day out, deepening its bed at the bottom and widening it at the top. But the wear upon the sides is not so great as down in the channel. The rub on the walls comes largely from what the River carries in its load—that is, sand, silt, and mud. The body of this silt is enormous again (the River bears to the sea each year more than three hundred million tons of it), but it has in itself no such grinding power as the stones and boulders hurled along in the bed. There is some slight wear on the walls from stones as well as silt, and eventually they break down; but, as we shall see presently, it is by the saw-through of lateral streams and the gradual cutting up of the walls into sections that they are disintegrated rather than by the River wearing along their faces.
So much by way of explaining the cutting of the inner walls—an explanation which the visitor will probably accept, since the Inner Canyon, or Granite Gorge, as it is called, does not bother him so much as the buttes, platforms, and walls that lie back from it and lead up to the Rim. Yet the River in its initial depression made possible all the breakdown and destruction of the side walls and canyons and all the carving out of platforms and buttes. Water seeks its level, and wherever there is a sink or valley or depression of any kind, there the streams will pour their gathered forces. The deeper the Colorado digs its bed the swifter the descent and cut-through of the lateral or side streams.
It should be repeated and emphasized that no stream wears its banks or walls evenly and smoothly by direct rubbing—at least, that is not the way banks and walls are broken down in this Canyon country. The main stream is like the trunk of a tree. It has many limbs that run off into smaller branches, that in turn trail away into twigs and shoots. The walls of the primary canyon are cut through at intervals by side-streams that have produced secondary canyons; these in turn are cut at right angles by smaller tertiary streams and canyons, and so on into infinite ramifications. The plateau areas are drained through these subsidiary channels into the main trunk-river-the Colorado. As a result of this drainage system the plateau is sawn asunder by streams. Promontories, points, pinnacles, buttes are left outstanding, and, in turn, these are attacked, as the main areas were attacked, by small streams that eventually break them down.
Perhaps you will contend that there are no lateral or side streams coming into the Colorado because there is no running water in sight. Even on the maps one sees only the Little Colorado flowing in from the southeast, and a stream called Kanab Creek coming down from the northeast that almost runs out in dry weather. But there are ten thou-sand streams not on the map that run with every rain-storm. Look down into any side-canyon and you will see their dry beds. Every one of these side-canyons was produced by the stream that runs in its depth when there is a heavy shower.
It is a mistake to suppose these creeks unimportant because they do not have continuous flowing water. On your way down to the River by the Bright Angel Trail you will find, below the Indian Garden, a canyon cut out of the hard Archaean rock by the water that runs here after rains. Across the River you can see the enormous gorge called Bright Angel Canyon made by the drainage stream there. On either side of it you may count a succession of extended points, and between each pair of points is a tertiary stream draining the adjacent area. Once more, when you go down to Hermit Creek Camp you will notice half-way down the trail the heading of the creek and the great slash that it has made through the Red Wall. You may follow down that little creek several miles to the Colorado, and perhaps be surprised at its course through the rock (Plate 6), at its upright walls, its contributory side-canyons, its water-worn caves, its gouged-out bed. Another matter of surprise is the finding of huge boulders in the bed that did not drop down from the walls overhead, for they are a different kind of rock. They were rolled and carried down from the Red Wall, the Supai, and the Kaibab strata far back toward the Rim. At the mouth of the creek where it joins the River you will find the rocks of all the strata in all sizes and in all states of wear, flung together in confusion—flung by the swift waters of this little tributary.
Hermit Creek is a continuous stream, but in fair weather it is a small brook running clear, clean water that seems quite harmless. In summer you can step across it almost anywhere. It is not this quiet phase of it that is responsible for the rock-carving of its canyon, but rather its turbulent stage when, swollen with rains, it rushes along as a mountain torrent. All the side-arroyos then empty water, stones, gravel, and sand into it and increase the downward rush. Every hollow in between the little divides lying off at the sides of the creek contains one of these washes. They are usually and normally dry, but during periods of rain their flow may be very great. For example, back of the Hermit
Camp buildings you will find a large arroyo leading to the east, and if you follow it up you will notice evidence everywhere, not only of much water-wear, but of tremendous power in the intermittent stream. Boulders weighing many tons have been flung about and lodged in hollows, beds of coarse stone and gravel are washed and heaped up in mounds, leaps over high ledges are frequent, and basins beneath them offer proof positive of great water-wear. There is no doubt about either the size or the force of such a stream in wet weather.
Once more, it is difficult to exaggerate the cutting, rolling, rending power of these storm-streams (Plate 9). You may be astonished by the steep descent of the Colorado—the descent that made possible its deep-cut bed—but that is slight compared with the downward pitch of some of the side-f streams. Shinumo Creek, reached by the Bass Trail to the west of Hermit Creek, is twelve miles long, and in that distance falls five thousand four hundred feet, or four hundred and fifty feet in a mile.* That in times of great rain argues a torrent of terrific power.
The stream, big and little, has wrought havoc in this Plateau Country. Its windings and workings must be followed a little farther, for it is responsible not only for the Canyon and the Granite Gorge but for all the forms of the walls, the rims, the buttes, the promontories. Erosion here is the master-movement.