Popular Science Monthly/Volume 7/September 1875/Physical Features of the Colorado Valley II
|←Scientific Culture|| Popular Science Monthly Volume 7 September 1875 (1875)
Physical Features of the Colorado Valley II
By J. W. Powell
|A Popular Verdict: Robert Knox→|
II.—Cliffs and Cañons.
SOUTH of the Uinta Mountains, and beyond the hog-backs on either side of the liver, is a district known to the Indians as Wa-ka-ri'-chits, or the Yellow Hills. This country is elaborately embossed with low, rounded, naked hills. The rocks from which they are carved are yellow clays and shales. Some few of the shales are slate-colored, others pink; none so glaring and brilliant as the Bad-Lands of Black's Fork, but the tints are soft and delicate. The whole country is carved by a net-work of water-ways, which descend rapidly toward Green River, and the intervening hills are entirely destitute of vegetation. Looking at it from an eminence, and in the light of the mid-day sun, it appears like a billowy sea of molten gold.
To the south of these Yellow Hills, and separated from them by a gently-curved but well-defined ridge of upturned sandstone, there is a broad stretch of red and buff-colored Bad-Lands. Some of the beds are highly bituminous, and a fresh fracture reveals a black surface, but usually they weather gray. Where these bituminous rocks are found, hills and mesas are seen, covered, more or less, with vegetation, and the Bad-Land forms disappear. Still farther to the south, across White River, we find a continuation of these beds, but here more shaly, and interstratified with harder beds, and the alcove structure appears, somewhat like that in the Alcove Land near Green River Station. These White River alcove lands were, by General Hughes, named "Goblin City,"
The Terrace Cañons and Cliffs.—A few miles south of the mouth of the Uinta, Green River enters the Cañon of Desolation. The walls of this gorge steadily increase in altitude to its foot, where it terminates abruptly at the Brown Cliffs; then the river immediately enters Gray Cañon, with low walls, steadily increasing in altitude until the foot is reached, where it terminates abruptly at the Book Cliffs. In like manner the walls of Labyrinth Cañon are low above, and increase in altitude as we descend the river, until the cañon terminates, as those above, in a line of cliffs. To these last we have given the name Orange Cliffs. We sometimes call these the Terrace Cañons. They are cut through three great inclined plateaus.
Conceive of three geographic terraces, many hundred feet high, and many miles in width, forming a great stairway, from the Toom' pin Wu-near' Tu-weap' below, to the valley of the Uinta, above. The lower step of this stairway, the Orange Cliffs, is more than 1,200 feet high, and the step itself is two or three score miles in width. The second step, the Book Cliffs, is 2,000 feet high, or more, and a score of miles in width. The third, or upper step, is more than 2,000 feet high. Passing along this step, for two or three score miles, we reach the valley of the Uinta; but this valley is not 5,000 or 6,000 feet higher than the Toom'-pin Wu-near' Tu-weap', for the stairway is tipped backward.
Climb the Orange Cliffs, 1,200 feet high, and go north to the foot of the Book Cliffs, and you have gradually descended, so that at the foot of the Book Cliffs you are not more than 100 feet above the foot of the Orange Cliffs. In like manner the foot of the Brown Cliffs is but 200 feet higher than the foot of the Book Cliffs, and the valley of the Uinta is not quite 300 feet higher than the foot of the Brown Cliffs.
To go by land from the valley of White River to the Toom'-pin Wu-near' Tu-weap', you must gradually, almost imperceptibly, climb as you pass to the south, for a distance of forty or fifty miles, until you attain an altitude of 2,500 or 3,000 feet above the starting-point. Then you descend from the first terrace, by an abrupt step, to a lower. Still continuing to the south, you gradually climb again, until you attain an altitude of more than 1,000 feet, when you arrive at the brink of another cliff, and descend abruptly to the top of the lowest terrace. Still extending your travels in the same direction, you climb gradually for a third time, until you reach the brink of the third line of cliffs, or the edge of the escarpment of the lower terrace, and here you descend by another sudden step to the plane of the river, at the foot of Labyrinth Cañon. In coming down by the river, of course you do not ascend, but you pass these terraces along the plane of the river, the upper terrace through the Cañon of Desolation, the middle terrace through Gray Cañon, and the third through Labyrinth Cañon.
The bird's-eye view (Fig. 1) is intended to show these topographic features. The escarpment below, and in the foreground, represents the Orange Cliffs, at the foot of Labyrinth Cañon; the second escarpment, the Book Cliffs, at the foot of Gray Cañon; the third, away in the distance, the Brown Cliffs, at the foot of the Cañon of Desolation. It will be seen that the three tables incline to the north, and are abruptly terminated by cliffs on the south. For want of space the whole view is shortened.
In the three Cañons there are three distinct series of beds, belonging to three distinct geological periods. In the Cañon of Desolation we have Tertiary sandstones; in Gray Cañon, Cretaceous sandstones, shales, and impure limestones; between the head of Labyrinth Cañon and the foot of Gray Cañon, rocks of Cretaceous and Jurassic Age are found, but they are soft, and have not withstood the action of the water so as to form a cañon.
These formations differ not only in geological age, but also in structure and color. It will be interesting to notice how these structural differences affect the general contour of the country, and modify its scenic aspects.
In the description of the three cañons in the history of their exploration, the attentive reader has already noticed the great variety of geological and topographic features observed as we passed along.
Let us now take a view of the three lines of cliffs. The Brown Cliffs are apparently built of huge blocks of rock, exhibiting plainly the lines of stratification. The beds are usually massive and hard, and break with an angular fracture. The whole is very irregular, and set with crags, towers, and pinnacles. The upper beds of the Book Cliffs are somewhat like those last described, and they form a cap to extensive laminated beds of blue shales, in which we see exhibited the curious effects of rain-sculpture. The whole face of the rock is set with buttresses, and these are carved with a fretwork of raised and rounded lines, that extend up and down the face of the rock, and unite below in large ridges. The little valleys between these ridgelets are the channels of rills that roll down the rocks during the storms, and from one stand-point you may look upon millions of these little water-ways.
Labyrinth Cañon is cut through an homogeneous sandstone. The features of the cañon itself have been described, but the cliffs with which it terminates present characteristics peculiar to themselves. Below, we have rounded buttresses, and mounds and hills of sand, and piles of great, angular blocks; above, the walls are of columnar structure, and sometimes great columns, seen from a distance, appear as if they were elaborately fluted. The brink of this escarpment is a well-defined edge. But if these formations extended over the underlying beds at one time, and if they have been carried away by rains and rivers, why has not the country between been left comparatively level, or embossed with hills separated by valleys? It is easy to see that a river may cut a channel, and leave its banks steep walls of rocks; but that rains, which are evenly distributed over a district, should dig it out in great terraces, is not so easy to perceive.
The climate is exceedingly arid, and the scant vegetation furnishes no protecting covering against the beating storms. But though little rain falls, that which does is employed in erosion to an extent difficult to appreciate by one who has only studied the action of water in degrading the land in a region where grasses, shrubs, and trees, bear the brunt of the storm. A little shower falls, and the water gathers rapidly into streams, and plunges headlong down the steep slopes, bearing with it loads of sand, and for a few minutes, or a few hours, the district is traversed by brooks and creeks and rivers of mud. A clear stream is never seen without going up to a moister region on some high mountain, and no permanent stream is found, unless it has its source in such a mountain. In a country well supplied with rains, so that there is an abundance of vegetation, the water slowly penetrates the loose soil, and gradually disintegrates the underlying solid rock, quite as fast as, or even faster than, it is carried away by the wash of the rains, and the indurated rock has no greater endurance than the more friable shales and sandstones; but, in a dry climate, the softer rocks are soon carried away, while the harder rocks are washed naked, and the rains make but slow progress in tearing them to pieces.
When a great fold emerges from the sea, or rises above its base level of erosion, the axis appears above the water (or base-level) first, and is immediately attacked by the rains, and its sands are borne off to form new deposits. It has before been explained that the emergence of the fold is but little faster than the degradation of its surface, but, as it comes up, the wearing away is extended still farther out on the flanks, and the same beds are attacked in the new land which have already been carried away nearer the centre of the fold. In this way the action of erosion is continued on the same bed from the upturned axis toward the down-turned axis, and it may and does often happen that any particular bed may be entirely carried away, with many underlying rocks, nearer the former line, before it is attacked near the latter. Now, as the beds are of heterogeneous structures, some hard and others soft, the harder beds withstand the action of the storms, while the softer beds are rapidly carried away.
The manner in which these beds are degraded is very different. The softer are washed from the top, but the harder are little affected by the direct action of the water—they are torn down by another process. As the softer beds disappear, the harder are undermined, and are constantly breaking down; are crushed, more or less, by the fall, and scattered over, and mingled with the softer beds, and are carried away with them. But the progress of this undermining and digging down of the cliff is parallel with the upturned axis of the fold, so that the cliffs face such an axis.
When the fold is abrupt, so that the rocks on either side are made to incline at a great angle, ridges are formed, and this topographic structure of a country may be found even in a land of rains, though the ridges will usually be low, rounded, and more or less irregular, while in a dry climate they will be steep and regular, and will usually culminate above in a sharp edge; but where the rocks are slightly inclined, terraces will be formed, with well-defined escarpments.
It is interesting to note the manner in which the textures of these hard capping rocks affect the contours of the cliffs. When the hard rocks are separated into well-defined layers, or beds, the cliffs will be more or less terraced, as the strata vary in hardness. This is well
seen in the Brown Cliffs and the upper portion of the Book Cliffs. In the last-mentioned escarpment the harder beds are underlaid by soft, bluish shales, which appear below in the beautifully-carved buttresses.
In the Orange Cliffs there are a thousand feet of homogeneous light-red sandstone, and this is underlaid by beds of darker red, chocolate, and lilac-colored rocks, very distinctly stratified. The dark-red rocks are very hard, the chocolate and lilac are very soft, so below we have terraced and buttressed walls and huge blocks scattered about, which have fallen from the upper part of the escarpment. The homogeneous sandstone above is slowly undermined—so slowly that, as the unsupported rocks yield to the force of gravity, fissures are formed parallel to the face of the cliff. Transverse vertical fissures are also formed, and thus the wall has a columnar appearance, like an escarpment of basalt, but on a giant scale; and it is these columns that tumble over at last, and break athwart into the huge blocks which are strewed over the lower terraces.
The drainage of an inclined terrace is usually from the brink of the cliff toward the foot of the terrace above, i. e., in the direction of the dip of the strata. As the channels of these intermittent streams approach the upper escarpment, they turn and run along its foot until they meet with larger and more permanent streams, which run against the dip of the rock in a direction opposite the course of the smaller channels, and these latter usually cut either quite through the folds, or at least through the harder series of rocks which form the cliffs.
In some places the waters run down the face of the escarpment, and cut narrow cañons, or gorges, back for a greater or less distance into the cliffs, until what would, otherwise, be nearly a straight wall, is cut into a very irregular line, with salients and deep reëntering angles.
These cañons which cut into the walls also have their lateral cañons and gorges, and sometimes it occurs that a lateral cañon from each of two adjacent main cañons will coalesce at their heads, and gradually cut off the salient cliff from the ever-retreating line. In this way buttes are formed. The sides of these buttresses have the same structural characteristics as the cliffs from which they have been cut. So the buttes on the plains below the Orange Cliffs are terraced and buttressed below, and fluted and columned above. Often the upper parts of these buttes are but groups of giant columns.
The three lines of cliffs, which I have thus described, have been traced to the east but a few miles back from the river. The way in which they terminate is not known; but, from a general knowledge obtained from a hasty trip made through that country, it is believed that they are cut off by a system of monoclinal folds. To the west they are known to gradually run out in plateaus and mountains, which have another orographic origin.
Climb the cliff at the end of Labyrinth Cañon, and look over the plain below, and you see vast numbers of buttes scattered about over scores of miles, and every butte so regular and beautiful that you can hardly cast aside the belief that they are works of Titanic art. It seems as if a thousand battles had been fought on the plains below, and on every field the giant heroes had built a monument, compared with which the pillar on Bunker Hill is but a mile-stone. But no human hand has placed a block in all those wonderful structures. The rain-drops of unreckoned ages have cut them all from the solid rock.
Between the foot of Gray Cañon and the head of Labyrinth Cañon we descend through many hundred feet of soft shales, sandstones, marls, and gypsiferous rocks of a texture so friable that no cañon appears along the course of the Green, but, along the southern border of the terrace above the Orange Cliffs, buttes of gypsum are seen. Sometimes the faces of these buttes are as white as the heart of the alabaster from which they are carved, while in other places they are stained and mottled red and brown.
As we come near to the Book Cliffs the buttes are seen to be composed of the same beds as those seen in the escarpment, and we see the same light-blue buttresses and terraced summits.
On the terrace above the Book Cliffs, the buttes are less numerous, but the few seen have the angular, irregular appearance of the Brown Cliffs.
The summit of the high plateau through which the Cañon of Desolation is cut, is fretted into pine-clad hills, with nestling valleys and meadow-bordered lakes, for now we are in that upper region where the clouds yield their moisture to the soil. In these meadows herds of deer carry aloft with pride their branching antlers, and sweep the country with their sharp outlook, or test the air with their delicate nostrils for the faintest evidence of an approaching Indian hunter. Huge elk, with heads bowed by the weight of ragged horns, feed among the pines, or trot with headlong speed through the undergrowth, frightened at the report of the red-man's rifle. Eagles sail down from distant mountains, and make their homes upon the trees; grouse feed on the pine-nuts, and birds and beasts have a home from which they rarely wander to the desert lands below. Among the buttes on the lower terraces rattlesnakes crawl, lizards glide over the rocks, tarantulas stagger about, and red ants build their play-house mountains. Sometimes rabbits are seen, and wolves prowl in their quest; but the desert has no bird of sweet song, and no beast of noble mien.
The Toom'-pin Wu-near' Tu-weap'.—We now proceed to the discussion of Stillwater Cañon, Cataract Cañon, and Narrow Cañon, and the region of country adjacent thereto.
At the head of Stillwater Cañon the river turns to a more easterly course, and runs into a fold, which has a northeast and southwest axis, but its central line is never reached. Before coming to it the river turns again to the west, and runs entirely out of the fold, at the mouth of the Dirty Devil River. It will thus be seen that the dip of the formations under discussion is to the northwest. Going down to the middle of Cataract Cañon, we constantly see rocks of lower geological position appearing at the water's edge; and, still continuing from that point to the foot of Narrow Cañon, the same beds are observed in reverse order; that is, we see at the water's edge rocks of later geological age.
Where the upturned axis of this fold is situated is not known; but, looking away to the southeast, mountains are seen—the Sierra La Sal and Sierra Abajo. Looking over the general surface of the country, it appears that the course of the river is from lower into higher lands and then back again. Observing the present topographic features of the country, it seems strange that it did not find its way directly across from the foot of Labyrinth to the foot of Narrow Cañon, following the low lands. Why should it leave this low region, and run away out into the slope of a system of mountains, and then return? We must remember that the river is older than the mountains and the cliffs. We must not think of a great district of country, over which mountains were piled, or built, or heaved up, and that when rain fell it gathered into streams along the natural depressions of such a country and thus attempt to account for the course of the river; but we must understand that the river cut its way through a region that was slowly rising above the level of the sea, and the rain washed out the valleys, and left rocks and cliffs standing, and the river never turned aside from its original course to seek an easier way, for the progress of uplifting was not greater than that of corrasion. Again we see how slowly the dry land has emerged from the sea; no great convulsion of Nature, but steady progress.
The Orange, Cliffs, which terminate Labyrinth Cañon, extend to the west a few miles, and then change their course to the southwest, running parallel with the axis of the fold we are now discussing, and they cross the Dirty Devil a few miles above its mouth. Thus they are seen, like the other lines of cliffs, to face the axis of a fold. Fig. 2 is a bird's-eye view of this country, showing the course of the river through Stillwater, Cataract, and Narrow Cañons. It represents the cutting of the stream into the slope of a mountain-range, and out of it again, without crossing the range. On the left it shows two lines of cliffs. Here we have a district inclosed within Titanic walls. On the southeast are great mountains, and from the foot of their slope, on the north side, near Grand River, we find a line of cliffs crossing this stream, and extending to the Green, in a westerly direction; then to the southwest, to the Dirty Devil River, and then broken and confused by buttes and cañon-walls, which extend toward the east, until it strikes the southern foot of the mountains. Within this walled area a profound gorge—Cataract Cañon—is seen, with Stillwater Cañon above, and Narrow Cañon below. The lower cañon of the Grand is also seen, and a number of lateral cañons.
Along the general slope of the district between the cañons are vast numbers of buttes. Their origin is the same as that of the buttes previously described. Often they are but monuments, or standing columns of rocks. From them is derived the Indian name Toom'-pin Wu-near' Tu-weap'—"the Land of Standing Rocks."
Adjacent to the larger cañons, especially near the junction of the Grand and Green, walled coves are found. Each main gulch branches into a number of smaller gulches above, and each of these smaller gulches heads in an amphitheatre. The escarpments of these amphitheatres are broken and terraced, and in many places two such amphitheatres are so close together that they are separated only by a narrow gorge of vertical homogeneous sandstone.
This latter, though homogeneous in general structure, is banded with red and gray, so that the walls of the amphitheatres seem painted. In many places these walls are broken, and the coves are separated by lines of monuments. Where these coves or amphitheatres are farther apart, the spaces above are naked, presenting a smooth but billowy pavement of sandstone, in the depressions of which are many water-pockets, some of them deep, preserving a perennial supply; but the greater number so shallow that the water is evaporated within a few days after the infrequent showers.
In many places, especially in the sharp angles between gulches, the rocks are often fissured, and huge chasms obstruct the course of the adventurous climber.
These cañons, and coves, and standing rocks, and buttes, and cliffs, and distant mountains, present an ensemble of strange, grand features. Weird and wonderful is the Toom!-pin Wu-near' Tu-weap'.
Marble Cañon.—The escarpment, which we call the "Vermilion Cliffs," at the foot of Glen Cañon, exposes the same beds as are seen in the face of the Orange Cliffs, at the foot of Labyrinth Cañon. It will be remembered that the beds exposed in the Terrace Cañons dip to the north. Between the Orange Cliffs and the Vermilion Cliffs, the strata are variously dipped by monoclinal folds, having their axes in a northerly and southerly direction, and the red beds are at about the same altitude above the sea at the two points. The Vermilion Cliffs which face the south form a deep, reëntering angle at the mouth of the Paria. On the east side of the Colorado, the line stretches to the southeast for many miles; on the west side, it extends, in a southwesterly direction, about fifteen miles, then turns west, and, at last, to the northwest. The general northerly dip is again observed from the mouth of the Paria to the mouth of the Colorado Chiquito.
The general surface of the country between the two points is the
summit of the Carboniferous formation. At the mouth of the Paria this is at the water's edge; at the mouth of the Colorado Chiquito it is 3,800 feet above the river. The fall of the river, in the same distance, is about 600 feet, so that the whole dip of the rock between the two points is about 3,200 feet. The distance, by river, is sixty-five miles; in a direct line, twenty miles less. So we have a dip of the formation of 3,200 feet in forty-five miles, or about seventy feet to a mile.
The slope of the country to the north is the same as the dip of the beds, for the country rises to the south as the beds rise to the south.
Stand on the Vermilion Cliffs, at the head of Marble Cañon, and look off down the river over a stretch of country that steadily rises in the distance until it reaches an altitude far above even the elevated point of observation, and then see meandering through it to the south the gorge in which the river runs, everywhere breaking down with a sharp brink, and in the perspective the summits of the walls appearing to approach until they are merged in a black line, and you can hardly resist the thought that the river burrows into, and is lost under, the great inclined plateau.
- From "Report on United States Geological and Geographical Survey of the Territories, Second Division." Major J. W. Powell in charge.