THE first five hundred feet of wall at the Canyon is called the Kaibab limestone. It can be seen exposed in cliff form anywhere under the Rim. It belongs to the late Carboniferous period* and shows shell life in many of its exposures. Fossil Mountain, just beyond Havasupai Point, is thickly strewn with these shells, but they may also be seen in the broken boulders along the Bright Angel Trail a hundred feet below the edge.
On the face-walls of the Kaibab rain and wind hollow out many recesses and small caves, though the general appearance of the cliff is smooth and rather abruptsometimes uncomfortably so. For this is the “precipice” of the one-day visitor. The steep descent, however, is seldom for more than two hundred feet. Then the wall breaks down into a rough talus where huge blocks are heaped, trees and bushes struggle for existence, grasses grow in the rock crevices, and flowers sway along the narrow ledges and platforms. Sometimes harder portions of the walls are seen standing out from the wall itself as turrets and pinnacles. A hard cap of crystalline limestone usually protects the top of the turret from rain while the winds carve the main shaft into fantastic form. These pinnacles are sometimes known as “dead men” or “hoodoos” or “monuments” and are seen in many places along the Rim. Thor’s Hammer, on the way to Grand View, is the popular illustration.
The Kaibab is seen not merely from El Tovar but from every view-point at the Canyon. Across on the north side it appears in greater thickness than near the hotel. Some of the larger buttes seen in the Canyon show it. The top cap of the so-called Temple of Vishnu, and also of Wotan’s Throne, is made up of it. These limestone walls with their pale-yellow, cream-colored, and warm salmon tones undergo great changes with the shifting sunlight, especially at sunrise when they become golden, or at sunset when they glow with a fire orange, or at twilight when they appear amethystine. They are beautiful walls at all times and bear their part as a top cap to the Canyon strata with dignity and grandeur.
Directly under the Kaibab comes the Coconino sandstone, a buff-colored strata some four hundred feet thick. This is often cross-beddedthat is, laid down in drifts that are at loose angles to each otherbut it makes up a stubborn rock and a steep wall. It is usually seen in perpendicular face with no talus or slope below it. Where it rests upon its underbasing of Supai formation (well shown at the left of Bright Angel Trail below the tunnel, or in the basin known as the Inferno) it fits as neatly and runs on as smoothly as though set up by a master mason. One is somewhat at a loss to understand how it could have been so evenly spread under the sea, how it could have been laid down so flat and flush upon the Supai as though done in a day, and how both strata were forced up into the open with-out bending, shattering, or breaking in any way. Was the rose gray put down on the Indian red over night, or was it deposited, like falling snow, through thousands of years, so softly, smoothly, and evenly, that today, after these many centuries, it lies as flat as the sea itself ?
There are no fossils in the Coconino sandstone and, being a supporting wall, there are few outlying domes, turrets, or pinnacles. Occasionally portions of the wall are split off by frost and there are many rounded holes in the face-wall that look as though drilled by instruments, but the only tools used were the wind and rain. Where the cross-bedding occurs there are minor faults and breaks which often result in caveswind-worn caves with graceful curves and rippled, fine-grained, sandy floors of the most beautiful golden-pink color. But for all its flexures and weatherings the Coconino stands upright with sheer faces that are vastly imposing in lift, bulk, and weight. It is an extensive wall and one of the most prominent in the Canyon strata, because of its light color and clean exposure. It runs like a wide ribbon under the Kaibab. Across the River you can see many miles of it stretching east and west with remarkable regularity. Crumbling remnants of it cap some of the lesser buttes in the Canyon such as Isis and Osiris.
The Supai formation of sandstone and shalethe third group of strata in the wallsis very marked in its Indian-red color, and because of its enormous bulk it has much to do in determining the general color-tone of the Canyon. The red of these sandstones and shales shifts and changes much under varying lights. In the early morning when in shadow it is beef-blood red; at noon it is a dark terra-cotta; at sunset almost a fire red. These shiftings and changes are well seen at morning and evening in the basins known as the Abyss and the Inferno, to the west of El Tovar. The local color in the wall is due to iron oxide. Many of the beautiful harmonies of gold and orange seen in the cliffs of the Canyon are caused by just such common things as iron oxidemere iron-rust.
The Supai is some twelve hundred feet in thickness and is seen from all points at the Canyon (Plate 11). From the hotel Rim the so-called Battleship (Plate 1), in its superstructure, is entirely made up of these sandstones and shales, though the base of it (seen from the trail below) is the Red Wall. The texture of the beds is a little loose and soft, and the walls wash down easily into slopes that are usually marked by descending steps, the treads of which are sandstone and the risers shale. The steps and ledges, indicating successive beds, look rather thin when seen from the Rim, but in reality they may be from ten to fifty feet thick. Rains with their consequent streams wash down and over them, creating valleys in the slopes, little canyons in the rock. The slopes are usually marked by a good many small pinyons, scrub-oaks, berry bushes, with grasses and flowers. Where the growth is scanty and the rock formation shows through, the repeated lines of the steps remind one of a Roman circus. The arena effect is present everywhere.
The Kaibab, the Coconino, the Supai, and the Red Wall all complement each other in their carvings, but with great variety in their appearances. The harder walls show the large arenas and the softer ones the small flutings. Both of them are superb in line. The Supai beds are more regular and graceful than the others, and individual layers can often be traced for miles in their wonderful serpentine windings. They were originally laid down in a shallow sea, and the red mud and sand of their composition were mainly washings from the neighboring shores.
This same red mud loosened by rains is today washing down from the Supai slopes upon the face of the Red Wall and staining that enormous under-lying stratum a bright salmon-red. Its local color, as already suggested, is a blue-gray; but this color shows only in recently fractured parts or where the Supai has disappeared from the top and the local hue is allowed to reassert itself. Like the other wall colors, that of the Red Wall varies with the light and takes on many manifestations. In form the wall is a huge base upholding the strata above it, is largely a limestone with some alternating beds of sandstone, and is very compact, showing no horizontal lines of parting or bedding. There is a small talus at the bottom of it, but this is not a slope breaking down from water-wear so much as a rock heap accumulated by fallen fragments from the face-wall. The cliffs are almost perpendicular, and from the upper edge a stone will drop clear and sheer to the bottom. The Red Wall is between five and six hundred feet thick and is considered one ofthe sturdiest strata in the Canyon. Receiving the accumulated waters from the upper slopes it wears back in enormous cirques or arenasgreat amphitheatres that might seat half a million people. The miner and the explorer still worry along its upper edge seeking some break in the face that will let them down to the River, but the Red Wall keeps its inaccessible front. The only break in the edge is where streams run over it and cut a pitcher lip, and the only fracture is where a geological fault is apparent. The trails to the River lead up or down it where it is faulted, as at Bright Angel and Hermit; but not otherwise. It is one continuous precipice, the most abrupt wall in the Canyon, with no weak line about it. When seen from below, the bulk of it is vastly impressive. It seems to be the underbasing of the globe rather than a simple sedimentary bed laid down under the sea and dotted with occasional cup-corals here and there.
For all its hardness and stanchness there are some hollows in the Red Wall, made by wind and rain, that take on the proportions of caves. Some-times the cut-back arenas in the face have projecting eaves or roofs over themthe wear being more rapid beneath than aboveand this produces an open-cave effect. Again, one finds in places huge sections fallen out in blocks leaving square cells or spaces under the wall. But these appearances are unusual. The Red Wall, generally speaking, symbolizes endurance and strength.
When the bottom of the Red Wall is reached we meet with trouble. The trouble is geologically called “unconformity.” There are strata missing herestrata that are due to appear and yet are not seen. The Carboniferous ends under the Red Wall, and the Devonian, Silurian, and Ordovician should succeed, but the last two are entirely missing and the Devonian appears only in isolated fragments here and there.
What became of these strata? Perhaps they never existednever were laid down here. The sea-bed may have risen when only the Cambrian series that now underlie the Red Wall were formed. That series may have been the top strata for many centuries, and then the whole plateau may have subsided beneath the sea and been covered by the strata of the Carboniferous. Who can now say?
But it is more probable that the land arose from the sea when the Devonian, Silurian, and Ordovician were in place and that these strata were eroded, washed away, before the subsidence in the sea that allowed the Carboniferous and later strata to be superimposed. There are theories on the subjectseveral of themheld by geologists and they are more or less tenable. Millions of years are stipulated for their working out. But neither the theories nor the ages are vitally important to us at this time. The main necessity is to recognize that three geological periods with several thousand feet of rock strata are gone between the Red Wall and the Muav limestonegone without changing the dip or greatly ruffling the surface of the underlying limestones on which the Red Wall now rests. Their disappearance we may count a Canyon mystery and let it pass at that.
The strata that now follow under the Red Wall belong to the Cambrian Period and are usually referred to as the Tonto Group (Plate 12). The first of the group is the Muav limestone. It underlies the base of the Red Wall and does not show to ad-vantage because the talus of the Red Wall rather hides it. On Bright Angel Trail it is inconspicuous, though there is as much as three hundred and fifty feet of it. It is thinly bedded, finely mottled, bluish in local color, but stained to a warm tan, or in places pale green, by exposure. Few fossils have been found in it, whereas the beds lying under it are marked with them. Geologists are interested in the Muav limestone, but its strata will hardly attract the attention of the average visitor.
Below this Muav limestone are the so-called Bright Angel shales which spread enormously be-cause they are soft, break down easily into slopes that flatten out and merge into a platform or terrace sometimes miscalled “the lower plateau.” The thickness of the shales is not more than three hundred and fifty feet, but their slopes spread down and out in places for great distances.
These Bright Angel shales are easily recognized anywhere and everywhere by their graceful rounded contours, their smooth water-worn slopes, their shallow arroyos and stream-beds, and, above all, by their Nile-green or yellow-green coloring. The color is refined and delicate and responds quickly to every change in sky and cloud. Some of the most beautiful color-harmonies at the Canyon come from the juxtaposition of these greenish shales with the salmon hues of the Red Wall above and the heliotrope and raspberry reds of the Unkar Group below.
The flattened slopes of these shales reach out and down toward the rim of the Inner Canyon, overlying in thin sheets or shingles the strata known as the Tapeats sandstone (Plate 30). A false sage-brush with sad-colored cacti grow upon them, wild burros use them for a stamping-ground, and coyotes, lizards, and snakes love their isolation. There are trails across them leading east and west in the Can-yon depths, and from them wonderful sights are to be seen. Not the least of the sights is the overlook into the Inner Canyon with the Colorado running like a mad mill-race twelve hundred feet below.
The Bright Angel shales are followed by two hundred feet of the Tapeats sandstone, coarse-grained, cross-bedded, and very stubborn in texture. Its side-canyons have abrupt walls that are as impossible of ascent or descent as the Red Wall. The layers of it seem thin and brittle, snapped off on the faces in sharp fractures, with shallow ledges that only the owls and the eagles seem to know intimately (Plates 5, 6). These beds of Tapeats sandstone are occasionally broken through on their backs in cubes or sections like a shattered pavement. The breaks develop with rains into sunken basins of enormous size with ragged-edged, inaccessible walls. At the base of buttes both the green shales and the Tapeats sandstones are frequently broken through and cut out by great water-wear, but the far points of the base or platform remain unbroken and extend out as star-shaped arms that appear like pedimental supports of the buttes themselves.
The thin slab-like layers of the Tapeats do not make a wall that is commanding in mass, though it bristles with difficulties for the climber. Nor is its color (a brown or buff; in places a dull maroon) very alluring. It is more curious than attractive be-cause of its age, its pebbly grit, and its wave markings formed under the sea. At its base, as also along its top, are many recesses or caves, some of them due to structure, some to stream-wear, and some to the seeping and falling of water through the rocks from above. Again, there are many crevices along its rim that seem to be bottomless. A stone thrown down them will rattle its way out of sight and hearing without coming to a halt. The Tapeats forms the cap to the rim of the Inner Canyon. It extends out to the edge and breaks off abruptly in a brown cliff over the old Archaean wall (Plate 5). So perpendicular is its face-wall that, once more, a stone can be tossed from the top into the stream below without difficulty.
Between the Tapeats and the old Archaean comes another gap in the geological record called “the great unconformity.” Some twelve thousand feet of the Algonkian system are here missing, but portions of itthe so-called Unkar and Chuar groups still remain in sections and wedges (Plate 11). Why and how they have survived is matter of theory in which geologists practically agree. The beds were originally laid down on the smooth, planed-off surface of what is called the old Archaean rock. This old rock is not exactly the original crust of the earth but a rock changed by heat, pressure, and intrusions from below. This metamorphosed rock and the beds lying upon it were bent into arches and hollows by deep-seated earth forces, and in places were broken into blocks. Some of the blocks were moved up and some sank down, the sedimentary beds in the down-dropped blocks being thus inlaid into the original floor. When erosion came, the greater part of the Algonkian system, including huge portions of the Unkar and Chuar, were worn off and carried away, but certain other portions, being perhaps protected by their inlaid position or being of harder fibre, remained intact. Afterward there was a subsidence under the sea of the whole area, and for many centuries the laying down of the Tapeats sandstone, with succeeding formations, took place on the eroded surface of the Archaean and around and over the remaining blocks and portions of the Unkar and Chuar groups. When, after the second upheaval, the Canyon was carved out, the surviving portions of the Unkar and Chuar appeared as detached sections surrounded by the Tapeats, or lying irregularly between the Tapeats and the schists of the old Archaean.
These Unkar and Chuar groups are known today as the Grand Canyon Series, and sections of them appear in half a dozen places in the Canyon. A portion of the Unkar shows across the River to the left of Bright Angel Canyon. The best view of it is from the Turtlehead on the Tonto platform, but it can be seen from the hotel Rim without a glass. Its distinctive mark is its raspberry-red color, tempered with a what-not of mauve, heliotrope, and violet. At the Turtlehead you are on a level with it looking across the River, and can see its irregular disposition, as well as its later surrounding and partial overlaying by the Tapeats sandstone. The section begins to show at the left, far down the River, under the foot of Isis Temple, and continues under the cliff wall of Cheops Pyramid. Straight across the River from you the light-colored shelf of the Tapeats breaks off and is succeeded on a lower shelf by the Unkar, which persists as far as Bright Angel Canyon. A little mound of the Unkara remnant left overappears on your side of the River to the right and above the last lap of the Bright Angel Trail; and above this mound there is a shelf of the same stratum almost on a level with the Tapeats.
The Unkar is, all told, the most precious piece of local color at the Canyon, and with the curious forms of the beds, slopes, and pits goes to make up a very unusual appearance. At Bright Angel the mauves, magentas, and vermilions of the slopes, the purples of the wave-shaped layers that come out to the edge, the old velvet quality of them all is very striking. At sunset these colors change to wonderful tones, especially if there are clouds above them that catch light and color from the west. With rains the colors change once more to brighter notes, and some of their splendor runs over the edge and down the face of the old Archaean rock, staining that an indescribable but unforgetable hue.
The largest outcrop of these Unkar beds is to the east of Grand View, where they extend as far as the mouth of the Little Colorado. There, too, the Chuar beds come into view with a more diversified coloring than the Unkar. But they are not accessible to the average Canyon visitor because the way there is a difficult one to travel.
The rocks composing these two groups are made up of limestones, sandstones, shales, quartzites, conglomerates, and were originally laid down as shallow-water deposits, the Unkar first and the Chuar later. They were greatly eroded, as we have already premised, after upheaval. Only the hard cores and the deposits protected by inlaid positions remained. These portions show no fossil life. Their continuance surrounded by the Tapeats sandstones or lying at odd angles on the Archaean or, as they are called, Vishnu) schists creates one of the most interesting of all the geological appearances at the Canyon.
With the crystalline schists that underlie the Unkar and Chuar beds we come to a swift transition. All the rocks of the Algonkian and Palaeozoic systemsthat is, all the rocks in the Canyon walls above the Archaeanare of sedimentary origin. They were deposited in flat beds under the sea and heaved upfor the most part with little break or fractureto their present horizontal positions. The Archaean schists, gneisses, and granites that make up the inner walls (or Granite Gorge) of the Can-yon are of very different structure (Plate 5). They do not lie in horizontal beds but are on end, gnarled, crumpled by pressure, fused by heat. The schists are metamorphic rocks entirely recrystallized by heat; the gneisses and granites are igneous or fire rocks. The fire-rocks lying beneath pushed up through and helped metamorphose or change the rocks above into schists, at the same time being themselves recrystallized and twisted into fantastic shapes that set as they cooled. The result is some twelve hundred feet of rock that in interest for the layman outstrips any in the Canyon.
The Archaean flanks both sides of the Colorado at Bright Angelthe River flowing through and over it. The sides are almost perpendicular, are rough in surface, and are accessible to the climber only in spots. The rock is very hardthe hardest in the Canyonis cast into slag forms by heat and pressure, and is not only worn and cut by water, but is broken by heavy boulders. The rim or edge is fluted like the Kaibab by streams that pour over it from the Tonto platforms, but the indentations are irregular, shallow, and not pronounced in curvature.
One cannot imagine anything more uncanny than these inner Canyon walls. They are appropriate lining for the interior of the Pit, and in places where they break down in conjunction with Unkar beds into huge pot-holes (notably near the foot of the Lincoln Point Trail) they are almost too ‘creepy for enjoyment. They are grim and unearthly, a mixture of everything that can be made by heat, fusion, intrusionthe flux of the great furnaces down below. No one knows how deep they lie. There are pale indications of old stratification about them, as though at one time they may have been bedded, but they have been so bent and blurred by heat that recognition is difficult. Perhaps they once lay on a great flat plain and the plain stretched out into infinite distance with a crystalline surface upon which was neither water, air, nor life. The newly formed world may have cooled down to such a surface. But that was before either the Colorado or the Canyon. Down here in the Granite Gorge you are not merely prehistoric and pregeologic; you may be looking at walls that date back to the cooling of the crust.
No doubt much of their strange appearance is due to their color. This is a dark purple varied by every imaginable shade of violet, warmed by reds that suggest dark rubies and garnets, streaked by broad intrusive bands of rose granite that wind in serpentines along the walls, and glittering with countless flakes and faces of mica. Seen at noonday under full sunlight it makes a most astounding spread of dark-reddish purple. The eye wanders over it bewildered by the great blend, the splendid glow of it, and yet fully conscious that infinite variety of color, rather than sameness, makes up its harmony. To add to the bewilderment the mica glintings give the wall in places a satiny sheen. And the bent and twisted strata keep beating into your eye and brain the story of firethe fire that perhaps once glowed in the Great Pit in the heart of the earth. It is a true enough Plutonian bed through which the red Colorado runs.