Geological Survey Bulletin 707 Guidebook of the Western United States: Part E. The Denver & Rio Grande Western Route

As most of the westbound travelers who pass through Denver stop over a few hours or a few days, it is desirable to call their attention to many side trips that may be made in one day by trolley, railroad train, or automobile.

Most people are attracted by the mountains, and the excursions that are generally of the greatest interest are those made into their narrow canyons or over their snowy summits. Not only are the mountain trips enjoyable on account of the scenery, but they enable the traveler to have the pleasure of tramping over snow banks under the hot rays of a midsummer sun, to see something of the mines of gold and silver and other metals that have made this region famous, and to behold the magnificent exposures of rock along the canyon walls and in the highest peaks and thus to learn some of nature's hidden mysteries regarding the earth upon which he lives.

CONTINENTAL DIVIDE AT CORONA IN ROLLINS PASS.

Corona is reached by the Denver & Salt Lake Railroad, or "Moffat road," as it is generally called. It is the objective point of most travelers who wish to enjoy the pleasure of snowballing on a hot summer day and of experiencing the sensation of standing on the backbone of the continent. On leaving Denver for this trip the traveler sees first the fine irrigated farms of Clear Creek valley (see Pl. III, A) and then the upturned beds of sandstone and shale which carry the coal of the Denver Basin. These rocks, which are called by geologists the Laramie formation, are of Cretaceous age, and their position in the geologic column is shown on page II. No coal beds can be seen from this railroad, but a few miles to the north there are extensive mines.¹

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¹Coal has been mined in Colorado continuously since 1864, 12 years before the Territory became a State. One of the first fields to be developed was that of Boulder County, which lies in the northern part of what geologists call the Denver Basin. This basin, though not a surface basin, is so called because the beds of rock in it dip toward and under the city from all directions, so that any one bed of rock, if it could be followed below the surface, would be found to have the form of an irregular basin. The western rim of the basin is formed of the rock beds that are upturned along the mountain front in the vicinity of Morrison, Golden, and Boulder, but the eastern rim is not conspicuous, as the beds dip very gently westward toward the center of the basin.

The coal is contained in sandstone and shale of Cretaceous age (Laramie formation) and probably underlies Denver itself, but here it is so far below the surface that it has been reached in only the deepest drillings. The coal is mined from slopes which go down on the outcrop of the coal bed or from shafts which are sunk nearer the center of the basin and which reach the coal at different depths.

The coal is what is now generally called subbituminous, a rank which is below that of the bituminous coals of the East. It is frequently called "black lignite," because of its color and because it has some of the properties of a lignite, or woody coal. The subbituminous coal does not soil the hands and is a desirable domestic fuel, but upon exposure to the weather it breaks up or "slacks"—the lumps fall to pieces and the coal becomes a heap of fine fragments. It contains a much higher percentage of water than the eastern coals, and this gives it a much lower fuel value. Notwithstanding these defects, subbituminous coal is extensively mined and finds a ready market throughout the Denver region.

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PLATE III. A (top), WHEAT FIELD IN CLEAR CREEK VALLEY. Water has transformed Clear Creek valley from a barren waste to rich agricultural land. Photograph by L. C. McClure, Denver; furnished by the Colorado & Southern Railway. B (bottom), MOUNTAIN FRONT ON THE "MOFFAT ROAD." The Denver & Salt Lake Railroad, in climbing the steep mountain front, tunnels through great slabs of dark-red sandstone upturned against the mountains. Between tunnels the traveler may obtain views of the plains stretching away to the east, farther than the eye can see, and of the low ridges that skirt the mountain at his feet. Photograph copyrighted by L. C. McClure, Denver; furnished by the Denver & Salt Lake Railroad.

At the loop which the railroad makes before it climbs the eastern front of the mountains there is exposed a dark shale (Benton shale or lower part of the Colorado group), which lies near the base of the Upper Cretaceous series. At Plainview the road cuts through a hogback² formed of the upturned edge of the underlying Dakota sandstone and shows some of the variegated sandstone and shale of the Morrison formation, which lies directly below the Dakota sandstone, or toward the mountains. The succession of rocks in the hogback and the mountain front is shown in figure 2. Beyond the valley formed in the soft rocks of the Morrison formation the red sandstone (Fountain formation) lies upturned against the mountain front in great triangular slabs like the teeth of a gigantic saw. (See Pl. III, B.) The railroad in climbing the mountain front pierces the projecting points of this hard layer by many short tunnels, and the traveler has ample opportunity to study its characteristics as the train turns and twists around the ravines or dives headlong through the rocky tunnels. (See Pl. IV, A). This red sandstone is tilted up against the gneiss (pronounced nice) or granite-like rock that forms the bulk of the Front Range.

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²A name applied in the Rocky Mountain region to a sharp-crested ridge formed by a hard bed of rock that dips rather steeply downward. One of the best examples of this kind of surface feature can be seen at Canon City, where the Skyline Drive follows the sharp crest of a hogback of Dakota sandstone for miles, as shown in Pl. XXXV (p. 73).

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FIGURE 2.—Dakota hogback and mountain front north of Plainview, as seen from the "Moffat road." The dash line indicates the boundary between the Morrison formation and the Carboniferous sandstone.

When these beds of sandstone were formed they consisted of horizontal layers of sand, which were laid down along the shore of a body of water, just as sand accumulates to-day along the shore of the ocean or of a large lake. The rocks upon which the sand rested were granite and gneiss, from which some of it was derived, and the sand lapped onto the shore irregularly, some beds extending much farther inland than others, the distance inland reached by them at one place or another depending on the form of the surface and the height of the water. Finally, after the entire region had been covered by layers that eventually became sandstone, shale, and limestone, the region on the west was lifted up hundreds or perhaps thousands of feet, and the red sand, which had hardened into sandstone, was bent upward in a great arch that may have extended entirely over the present Front Range. The streams probably cut away the upper part of this arch almost as fast as the land was raised, so that the mountains may never have been much higher than they are to-day. The work of the streams has been continued until all of the upper part of the sandstone arch has been removed, as shown in figure 3, and only the sharp upturn on the flanks, which can be seen so well from the "Moffat road," has been preserved.

FIGURE 3.—Arch of the Front Range restored. After Lee.

The train climbs steadily, affording here and there beautiful views far out over the plains to the east, and finally, when nearly above Eldorado Springs, it turns suddenly to the left and enters a tunnel that leads through the heart of the mountains. Beyond this tunnel the roadbed is in granite,³ and the banding of this rock gives little indication of the real structure of the mountain range. The streams have cut deep canyons, and many interesting views may be seen on the right of the train as it passes from branch to branch of South Boulder Creek, here crossing a canyon on a high trestle and there plunging into the darkness of a tunnel through a spur. Where South Boulder Creek is first seen it lies far below the level of the road, but its bed slopes steeply headward and is finally crossed by the railroad well above the sharp canyon, which represents the latest period of stream cutting in this region. If the trip is made in July the traveler may have the pleasure of seeing in the foothills acres of the beautiful Rocky Mountain columbine (Pl. IV, B), which has been adopted as the floral emblem of Colorado. The plant grows about 3 feet high, and each stalk bears a number of delicate lavender-tinted blossoms which become white as the season advances.

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³Wherever the crystalline rocks of the mountains are referred to in this guide they are called granite, though they really consist of granite, gneiss, and schist. In some places the rock may be entirely granite, and in others it may be gneiss or schist; but at many places these three kinds of rock are intimately mixed, showing that they may be different forms of the same rock.

G. P. Merrill describes gneiss (A treatise on rocks, rock weathering, and soils, pp. 142-145, New York, 1906) as follows:

"The composition of the gneisses is essentially the same as that of the granites, from which they differ only in structure and origin. * * * Structurally the gneisses are holocrystalline [entirely crystalline] granular rocks, as are the granites, but differ in that the various constituents are arranged in approximately parallel bands or layers. * * *

"In width and texture these bands vary indefinitely. It is common to find bands of coarsely crystalline quartz several inches in width, alternating with others of feldspar, or feldspar, quartz, and mica, or hornblende. A lenticular structure is common, produced by lens-shaped aggregates of quartz or feldspar, about and around which are bent the hornblende or mica laminae [layers]. The rocks vary from finely and evenly fissile through all grades of coarseness and become at times so massive as to be indistinguishable in the hand specimens from granites. * * *

"The origin of gneisses * * * is in many cases somewhat obscure, the banded or foliated structure being considered by some as representing the original bedding of the sediments, the different bands representing layers of varying composition. This structure is now, however, considered to be due to mechanical causes and in no way dependent upon original stratification. The name, as commonly used, is made to include rocks of widely different structure, which are beyond doubt in part sedimentary and in part eruptive but in all cases altered from their original conditions.

"This alteration * * * has been brought about not by heat and crystallization alone, but in many cases by processes of squeezing, crumpling, and folding so complex as almost to warrant the application of the term kneading. * * *

"In the present state of our knowledge it is in most cases impossible to separate what may be true metamorphosed sedimentary gneisses from those in which the foliated or banded structure is in no way connected with bedding and which may or may not be altered eruptives."

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PLATE IV. A (left), TUNNELS ON THE "MOFFAT ROAD." Tunnel succeeds tunnel in rapid succession on this railroad as it climbs the Front Range above Plainview. Photograph by L. C. McClure, Denver; furnished by Denver & Salt Lake Railroad. B (right), STATE FLOWER OF COLORADO. The Rocky Mountain columbine (Aquilegia coerulea) covers in midsummer many of the mountain slopes with its beautiful bloom. At first the outer petals are a delicate lavender or blue, but they soon fade to the purest white. Photograph furnished by the Denver & Rio Grande Western Railroad.

The first large village above the point where the railroad crosses South Boulder Creek is Rollinsville. Here the traveler sees no suggestions of mining, but if he could follow for a distance of 4 miles the road that climbs the hill on the north (right) he would find himself in a district that furnishes the metal for the filaments of most of the incandescent electric bulbs made in this country. This metal is tungsten, and a small percentage of it is contained in the steel from which most of the modern machine tools are made.

A few miles below Tolland the valley changes from a rocky V-shaped ravine to a broad valley having a U-shaped cross section. The meaning of such a change is shown in figure 4. The mountain valley shown in figure 4, A, has been carved only by the stream which occupies it. The walls slope gradually from the ridge on either side to the stream in its bottom, and the form of a section of such a valley, if cut directly across, would be a flat V. If after its excavation by the stream this same valley had been occupied by a glacier the ice would have ground away the projecting spurs on its sides and left it in the form shown in figure 4, B. The cross section of a valley is a nearly infallible indication whether the valley has been carved by running water alone or has been modified by ice. Thus the change from a V shape to a U shape a few miles below Tolland marks the point of farthest extension of the old glacier that had its source near the summit of James Peak and filled this valley with ice to a depth of many hundreds of feet if not a thousand feet. Usually the foot of a glacier of this magnitude is marked by a terminal moraine—a ridge of loose material carried down by the ice—but if such a moraine was ever built in this locality it has been washed away by the stream swollen with the waters of the melting ice.

FIGURE 4.—Diagrams showing effect of stream and glacial erosion. A, V-shaped valley cut by running water; B, same valley after it has been occupied by a glacier and reduced to a broad, flat U in cross section.

Although the valley at Tolland and for some distance above that place is broad and the slopes are smooth, it soon terminates abruptly at the foot of the Continental Divide, and no railroad can ascend it much farther and succeed in crossing the range. Consequently the engineers were forced to turn aside from what seems to be an easy pathway up the valley and construct the road to the summit in a roundabout way by scaling the valley walls. The train makes this climb with many turns and twists, and the traveler is generally deeply impressed with the care and precision with which the engineers fitted the roadbed to the mountain slopes. To the railroad engineer no slopes are too Steep for railroad construction, provided he can find ground sufficiently level to enable the road to curve around and double back upon itself, thus zigzagging its way up the mountain slope. The train climbs steadily upward, and one by one the ridges that from below seemed to be of great height are surmounted and they are found to be only low spurs of the still higher mountains above.

As the train nears the summit and encircles the little pond called Yankee Doodle Lake, the traveler may see some of the effects, other than the rounding of valleys, that the old glaciers have produced on the mountain scenery. In the canyons below, where the ice moved down in a great stream from the heights above, its effect was to smooth and round the slopes and to do away with much of the ruggedness that must have marked these canyons before they were occupied by the ice. Near the summit the ice scooped out in the side of the mountain great amphitheaters, called cirques, making the tops much more rugged than they were before. The circular depression that holds Yankee Doodle Lake is such a cirque, and all the vast rock slopes above the lake have been steepened by undercutting by the ice. Other cirques (such as those shown in Pl. V) may be seen in the mountains; indeed, the entire front above this place, up which the railroad finds, its way to the summit, consists of the walls of cirques that have united. The steepness of this slope is due almost entirely to the action of ice. In places the road is constructed along the upper edge of one of these great cirque walls, and the traveler may look down on the right nearly 1,000 feet into the cirque below. Although the cliff has an appreciable slope, it appears to be vertical especially when viewed from the moving train.

PLATE V. JAMES PEAK. This peak (13,260 feet) is one of the high points of the Continental Divide, a few miles south of Corona. The proposed tunnel of the "Moffat road" is to pass under it. Note the great amphitheater (cirque) which an ancient glacier has cut in the foreground on the right, and also the plateau-like character of the summit as shown in the distance. Photograph copyrighted by L. C. McClure, Denver; furnished by the Denver & Salt Lake Railroad.

At last the traveler reaches the summit, at Corona, 11,680 feet above the level of the sea, but the great snowsheds through which the train passes have prevented him from getting a fair view of the mountain summit. As soon as the train stops at Corona he may pass from the confinement of the snowshed and enjoy to the utmost the boundless space of the mountain top. On the crest in any direction there are peaks higher than Corona, the most prominent being James Peak (13,260 feet) on the south and Longs Peak (14,255 feet) on the north, but they can be seen from only a few points. On the west the traveler can look down on the billowy surface of Middle Park, one of the surface basins in the midst of the mountains; and on the east he can look over the wide expanse of spur and ravine up which the train has so laboriously climbed.

The railroad beyond Corona descends the fairly smooth western slope of the Front Range by many loops and turns until it reaches the floor of Middle Park. It crosses this immense basin in the heart of the mountains, cuts through the Gore or Park Range beyond in a deep, rugged canyon, and then continues westward across the great plateau country of north-western Colorado. The plateau contains one of the great coal fields of the State, which has only recently been developed. The coal is better than that of the Denver Basin, and much of it finds a ready market in the towns on the plains between Denver and Omaha.