Geological Survey Bulletin 612 Guidebook of the Western United States: Part B

SHEET No. 10. (click on image for an enlargement in a new window)

The section house called Harper (see sheet 10, p. 62) is built on a sandy shale in which have been found numerous fossil shells of Cretaceous marine mollusks. In the deep rock cut just west of the station may be seen a bed of coal about 3 feet 6 inches thick. This coal thickens toward the southwest, where it has been mined to some extent for local use.

Pine Ridge, so named because of a few scrubby piñons, or nut pines, that grow on the sandstone cliffs, consists of a light-gray cliff making sandstone that forms a prominent northward-facing ledge and belongs near the base of the Mesaverde formation. West of the cut are two prominent ridges formed by large reddish-brown limestone concretions that contain great numbers of marine shells. These are in the transition beds between typical Steele shale and the massive sandstone of the Mesaverde formation that lies on it. These transition rocks become gradually more sandy toward the west, and west of Rawlins they form a part of the Mesaverde formation.

Pine Ridge is the divide between the Laramie River drainage and that of Rock River. The waters of its eastern slope pass eastward through the Laramie Mountains and enter Platte River at Fort Laramie, 80 miles to the northeast. Those of the western slope flow through Rock River and Medicine Bow River to the Platte and thence through the Seminoe Mountains around the north end of the Laramie Mountains and after a circuitous route of about 250 miles join those of the eastern slope at Fort Laramie.

Just before reaching Rock River station the train crosses the river of the same name, and good exposures of the Steele shale may be seen in the bluffs in the north bank. Northwest of the town the railroad passes over a broad plain formed on this soft shale.

About 10 miles from Rock River the road crosses a low, sharp hogback of Niobrara limestone This chalky-white bed, 5 to 10 feet thick, forms a crest because it is harder than the shale above and below it.

Ridge takes its name from the prominent hogback ridge north of the station, formed by a hard sandstone in the Benton shale. The railroad parallels this ridge for a mile or more and then cuts through it west of the station. The lower part of the Benton shale is well exposed north of this sandstone ridge, in the center of the anticline formed by the arching of the strata. The route traverses this shale for about a mile before recrossing the sandstone and the Niobrara limestone and finally returns to the Steele shale in the northern limb of the arch.

Near Ridge the sandstone disappears because the fold that extends westward from the Laramie Range here plunges beneath the surface. Como Bluff, which lies north of Ridge station and which constitutes a part of this fold, consists of the Cloverly formation, the lower conglomeratic portion of which forms the crest of the bluff because of its superior hardness and forms also the long southward slope seen to the right from the train. Underneath this conglomerate occur in descending order the pink and blue shales of the Morrison formation which, because of the numerous shades of color, are often called the variegated beds; the Sundance formation containing numerous vertebrate and invertebrate fossils which prove its Jurassic age; and the Chugwater red beds.

The Morrison formation is probably the most interesting of those exposed here, because of the fossil bones of huge reptiles that it contains. The dinosaurs are described below by C. W. Gilmore, of the United States National Museum.¹ The largest animals that have ever been found lived at a time when reptiles were the ruling types of animals in the sea, on the land, and in the air. Flying reptiles similar to the one represented in Plate V, C (p. 21), were common, and the birds were so much like the reptiles that their remains can scarcely be distinguished.

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¹Como Bluff is classic ground to those interested in the fossil remains of animals that inhabited this region long ages ago, for it was here that the first dinosaur bones were discovered in the Rocky Mountain region. In 1876 Mr. W. H. Reed, now a professor in the University of Wyoming but then in the employ of the Union Pacific Co., found in the bluff above the new abandoned station of Aurora a large petrified limb bone, which he sent to Prof. O. C. Marsh, of Yale University. Prof. Marsh at once recognized the fossil as belonging to some unknown extinct animal and immediately enlisted the services of Mr. Reed. Collecting was actively carried on here for a period of ten years or more, and as a result of this work Prof. Marsh was able to publish the remarkable series of restorations of dinosaurs which appeared from time to time in several publications.

So famous did these fossils become that in 1899 the officials of the Union Pacific Railroad invited the geologists of the country to visit the places where the bones were found. An expedition consisting of geologists from universities and museums in many parts of the United States visited Como Bluff, the Freeze-out Hills, and other famous fossil localities. So well known are the bone beds at Como Bluff that some have called the beds the Como formation. However, in the same formation at Morrison, Colo., similar bones were found, and the formation was named Morrison—a name which is now generally accepted. Some of the dinosaurs were the largest land animals that ever walked the earth, and some were very diminutive. They differed greatly in size, shape, structure, and habits. Some were plant eaters; others fed on flesh. Some walked on four feet; others with small, weak fore limbs walked entirely upon the strongly developed hind legs. Some had reptile-like feet; others were bird footed. Some had toes provided with long, sharp claws; others had flattened hoof-like nails. There were dinosaurs with small heads and others with large heads. Some were large and cumbersome; others were small, light, and graceful and so much resembled birds in their structure that only the skilled anatomist can distinguish their remains. Some of enormous size were clad in coats of bony armor, which gave them a most bizarre appearance.

The largest herbivorous or plant-eating dinosaur whose fossil remains have been found in Como Bluff was the huge Brontosaurus, or thunder lizard, as it was called by Prof. Marsh. It was 70 feet long, stood 16 feet high at the hips, and had a long tail, an equally long neck, and a head that was only a little larger than that of a horse. The weight of such a creature has been variously estimated at 18 to 20 tons. This animal doubtless lived on the luxuriant tropical vegetation, but how its enormous bulk could be sustained by such food as could pass through its ridiculously small mouth has caused much wonder. It is not certain whether the name thunder lizard was given to it because of its size or because of the large sum—over $l0,000—which Prof. Marsh spent in excavating and preparing it.

Some dinosaurs that are even larger than the brontosaur have been found more recently. A Diplodocus now in the Carnegie Museum in Pittsburgh had the enormous length of 84-1/2 feet. The size of the fossil bones is indicated in the accompanying figure 9.

FIGURE 9.—Leg bones of a dinosaur, showing size in comparison with that of a man.

At the time these animals flourished the Rocky Mountain region was a low, nearly level country, covered with tropical vegetation, with many wide, shallow streams and swampy areas, thus furnishing a congenial place for these sluggish swamp-inhabiting creatures to wade lazily about or float in the water, for it has been deemed improbable that the enormous bulk of some of them could be sustained without lateral support such as would be obtained in water.

One of the most striking of the vegetarians of this period was the Stegosaurus, or plated lizard, so named because of the bony plates and spines with which its back was adorned. (See Pl. X, A.) Some of these plates, although very thin, were from 2 to 3 feet in diameter. They were held in upright position in two parallel rows on each side of the middle region of the back, extending from the base of the skull well down on the tail, the tip of which was armed with two pairs of long bony spines. In some individuals these spines were over 3 feet in length. All the plates and spines during life were covered by a thick, horny skin. The stegosaurs were about 20 feet long and stood about 10 feet high at the hips. The head was extremely small and lizard-like in shape, with a small brain, large eyes, and nostrils that indicate a considerable power of smell. The great disproportion in length between the fore and hind legs, the small pointed head, and the skin ornaments of plates and spines, made it so ugly that it may not have required other means of protection. Some passive protection, through repulsive ugliness or otherwise, seems to have been necessary, for its ludicrously diminutive brain suggests a mentality insufficient for conscious efforts at self-preservation. The want of brain capacity was compensated to some extent by an enlargement of the spinal cord near the hips that was about ten times as large as the brain.

PLATE X.—A (top), AN ARMORED DINOSAUR (STEGOSAURUS). The bones of this animal, which was about 10 feet high, were found in Morrison formation. B (bottom), A CARNIVOROUS DINOSAUR (ALLOSAURUS) PREYING ON ONE OF THE HERBIVOROUS DINOSAURS.

The life of these peaceable plant-feeding animals, however, was not always serene, for there lived at the same time dinosaurs whose powerful jaws armed with long, sharp teeth indicate that their food was flesh. These animals are called allosaurs. (See Pl. X, B.) That they fed upon large brontosaurs and smaller animals of their kind is indicated by the discovery of teeth of the carnivorous species together with the bones of their herbivorous contemporaries and of a skeleton of one of the herbivorous dinosaurs with bones scarred with tooth marks and grooves corresponding exactly to the sharp, pointed teeth of the allosaurs. The accompanying picture (Pl. X, B) depicts the remnants of such a prehistoric feast.

The allosaur was a most powerful animal, and skeletons over 20 feet long have been found. The large bones of the limbs were hollow, as were many other parts of the skeleton, this structure affording greater power of rapid movement. The feet were armed with long, sharp claws, especially the fore feet, which were well adapted for catching and holding prey or for tearing and rending skin and flesh.

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The stratified rocks in this region have been greatly affected by the disturbances that formed the mountains surrounding it. The region lies between the Laramie Mountain uplift on the east, the Medicine Bow uplift on the south, and the Seminoe and Shirley mountain uplift on the north. The strata between these mountains have been thrown into a series of folds and domelike arches, and in some localities profoundly displaced. A small dome that brings to the surface the Morrison and younger formations lies south of the railroad, but can not be recognized from the train.

The little town of Medicine Bow is well known to readers of Owen Wister's "Virginian" as one of the places where the cowboys played their laughable pranks, and the name of the novel has been taken by the hotel near the station. The name Medicine Bow is of Indian derivation, but how it came to be applied to the mountains from which the town takes its name is not certainly known. It is known, however, that some of the tribes annually visited the mountains that now bear this name to procure a certain kind of wood for their bows. In Indian talk anything that serves its purpose well is "good medicine," and according to report the mountains and streams where this timber was found became known as places where "good-medicine bows" were obtained.

The Flattop uplift, north of Medicine Bow, is a large, irregular-shaped dome, truncated by erosion and broken or faulted, as it is called, on the northwest side since it was formed. Carboniferous rocks appear at the surface in the center, and around these the younger formations crop out in concentric rings. The Freezeout Hills form a similar dome but expose granite in the center. Some of the smaller domes from whose crests the Cretaceous formations have not been removed by erosion may contain important oil pools.

The town of Medicine Bow is on a rolling plain formed by the erosion of the Steele shale. In this plain are numerous depressions in which water accumulates in wet weather, and as they have no outlet the water becomes alkaline, because it takes up the salts dissolved from the shale and left in the basins when the water previously collected there evaporated. These basins are similar to the alkali lakes of the Laramie Basin and are formed on the surface of the same shale formation. Such intermittent lakes are found in many places in Wyoming.

At Allen station, which is only a section house, the railroad passes from the Steele shale to the Mesaverde formation, which is here upturned and dips steeply toward the west. The softer layers, consisting of loose-textured sandstone and shale, have been eroded, leaving the harder layers to form sharp-crested ridges that are prominent along the road for a distance of about 4 miles west of Allen. The Mesaverde here has its full thickness, whereas at Pine Ridge the upper part had been eroded away before the Tertiary beds were laid down upon it.

Although the Mesaverde farther west is an important coal-bearing formation, little coal occurs in it here. A few thin seams less than a foot thick crop out near the road, but none of economic value have been found. The formation is characterized by two zones of hard sandstone separated by softer beds of shale containing fossil oysters and other shells of marine and brackish-water origin. These softer rocks have been eroded to form the depression which was crossed about 2 miles west of Allen, and which contains, north of the track, a small lake fed by sulphur springs at its west end.

From the crested ridges of the Mesaverde formation the traveler passes westward over a relatively smooth surface formed on the Lewis shale. The Lewis is a marine shale, somewhat sandy in places, and contains limestone concretions and great numbers of fossil shells, which belong to the Pierre fauna and indicate Upper Cretaceous age.

Como is a section house on the new cut-off between Allen and Dana. The original line, now abandoned, was built by way of Carbon, 4 miles south of Como. The new line not only shortens the distance and eliminates sharp curves and heavy grades but passes through Hanna, the center of an important coal-mining district. At Como the road is built through a small lake about a mile long, in which are found great numbers of salamanders that grow to be nearly a foot in length and are locally known as "fish with legs." These salamanders are rather common in southwestern United States and in Mexico, where they are used as food. The Mexican name for them is axolotl and the scientific name is Amblystoma mavortium.

About a mile east of Como the road passes from the Lewis shale to a younger formation, called "Lower Laramie," consisting of soft, easily eroded sandstone and shale containing fossil plants and shells of fresh-water invertebrates. West of the section house may be seen the yellow sandstones of the lower part of the "Upper Laramie" overlain unconformably by terrace gravels. From this locality westward for 5 miles the road is built on conglomerate, which is well exposed in a prominent hill to the left (south) of the track. It reaches the coal-bearing portion of the "Upper Laramie" in the Hanna Basin, a depression formed by mountain uplifts at the beginning of the Tertiary period and filled with conglomerate, sandstone, and coal-bearing shale. (See table on p. 56.)

Succession and character of the formations exposed in the Hanna coal field, between Como and Fort Steele, Wyo.

Hanna is a coal-mining town in the south-central part of the Hanna Basin. Two beds of coal are worked here, one 24 feet and the other 36 feet thick, according to the mine superintendent. They are separated by about 1,500 feet of strata in which one coal bed 18 feet thick has been opened and several thinner ones are known to occur. There are other coal beds below the lower or 36-foot bed that will be valuable sometime, but nothing has yet been done toward developing them.

Coal was discovered in this region by Frémont in 1843 on Platte River. The beds were opened there in 1856 and some of the coal was used in a forge. From 1862 until the Union Pacific Railroad was built these openings supplied coal for emigrants and for the Overland Stage Co. The presence of coal here was one of the reasons why the Union Pacific was built along the southern branch of the Overland Trail rather than along the northern branch up Platte River and over South Pass. Production of coal for the railroad began at Carbon in 1868, after the completion of the railroad westward to this point, and the coal of this field has furnished power for operating the road ever since that time.

The mines at Hanna were opened in 1890. Until 1902 this town was reached by a branch line, and Carbon, 10 miles to the southeast, furnished much of the coal for the road. But when the main line was diverted to pass through Hanna the town of Carbon was deserted and the mines there were closed.

The higher coal bed at Threetown, east of Hanna, lies rather close to the surface, and the falling of the roof in the abandoned parts of the mine makes bad surface sinks. One such hole about 150 feet across may be seen to the right, on the north side of the track, south of Threetown.

Hanna has a daily coal output averaging about 2,500 tons. The coal is subbituminous and is rather light and free burning. Under the forced draft of the locomotives cinders are thrown out and start numerous fires along the track. Burning grass and smoking ties are familiar sights along this part of the route, and even station buildings are sometimes set on fire. It is estimated that 500 square miles in this basin is underlain by coal and that 33,000,000,000 tons of coal is available for mining.

West of Hanna are several deep cuts in which the coal-bearing rocks may be seen to advantage. Conglomeratic sandstones which appear in two of these cuts dip eastward under the coal beds mined at Hanna. Farther west and lower in the formation there are a great number of coal beds, many of them thick enough to be of value for mining. These are all inclined about 20° toward the center of the basin and are warped and faulted in some places. The rocks here contain many fossils, including impressions of leaves, shells of fresh water clams and snails, and bones of dinosaurs, described below by C. W. Gilmore.¹ These fossils indicate a period of transition between the old Cretaceous life, in which reptiles were the dominant forms, and the newer Tertiary life, in which the mammals, the familiar class of vertebrates of the present time, predominated. The dinosaurs found here are the last known representatives of their type, and the mammals are primitive and inconspicuous. The plants, however, are of types not greatly variant from those of the present time, although the species are all different.

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¹Dinosaur bones belonging to the genus Triceratops (which means "three-horned face"), so named in allusion to the three horns with which the skull is armed, are found in the coal-bearing rocks of the Hanna Basin and ether formations of the same age. Over each eye was a massive horn directed forward and terminating in a long, sharp point, and the nose usually bore a third but much smaller horn. (See Pl. XI, B, p. 53.) A mounted skeleton of a Triceratops in the National Museum at Washington is about 20 feet long and stands 8 feet high at the hips. Some skulls that have been found measure more than 8 feet, over one-third the length of the entire animal. This great length of head is due largely to the remarkably bony development called the frill, which projects backward over the neck like a fireman's helmet.

PLATE XI.—A (top), A HORNED TOAD (PHRYNOSOMA CORNUTUM). A modern lizard about 3 inches long that is armed like some of the ancient dinosaurs. Horned toads are distributed generally over western North America and are especially abundant on the dry sandy plains. B (bottom), THE LAST OF THE DINOSAURS. This restoration illustrates the appearance of Triceratops, showing the great bony frill over the reptile's neck. From painting by C. R. Knight, made under the direction of J. B. Hatcher.

That Triceratops, although a plant eater, was a fighter and often engaged in combat appears to be shown by the broken and healed bones that have been found. A pair of horns in the National Museum bear witness to such an encounter. One of them has been broken and has healed to a rounded stump. Although Triceratops had an enormous head, it had a smaller brain in proportion to its size than the least intelligent land animal of the present time. In the earlier restorations of this animal as shown in the accompanying picture its skin has been represented as being smooth and leathery, but a recently discovered specimen, in which impressions of the skin are preserved, shows that it was made up of a series of hexagonal scales of various sizes.

Triceratops probably lived on leaves and branches of low trees or shrubs. At the time these animals existed, this part of the country was covered with vast swamps in which peat accumulated and wide watercourses that were constantly shifting their channels, the region presenting an appearance similar to that of the Everglades of Florida. Where the waters were not toe deep the region must have been covered by luxuriant vegetation and was inhabited by great numbers of the huge dinosaurs, as well as by smaller crocodiles, alligators, turtles, and diminutive mammals, all of whose fossil remains are now found embedded in the deposits of that time.

Contemporary with the Triceratops was a great duck-billed reptile related to Trachodon, which was the commonest dinosaur of an earlier period. An average-sized individual measured 30 feet from the tip of its nose to the end of its tail, and as it walked erect on its huge three-toed hind feet the top of the head was 12 or 15 feet above the ground. The head was nearly a yard in length, and the fore part of the skull was expanded to form a broad beak that was covered with a horny sheath, as in birds and turtles. This was admirably suited to the pulling up of the rushes and other water plants that constituted the feed of this great creature. These trachodont reptiles lived in the swamps and rivers.

The webbed fingers of the fore feet indicate swimming ability, and the long, deep, compressed tail must have been an efficient swimming organ, and was also useful as a counterbalance to the weight of the body when the animal walked on its hind legs. From specimens showing impressions of the skin it is known that the animal was covered with an epidermis made up of tubercles or knoblike plates, of two sizes, the larger ones predominating on the back and sides. One of the most remarkable features about this reptile was its mouth, which was armed with 2,000 or more separate teeth arranged in vertical rows. Each jaw has from 45 to 60 rows and from 10 to 15 teeth in each vertical row. These were self-adjusting, and as one was lost or worn out another pushed up to take its place.

As in Morrison time, so in the very much later Lance epoch there were armored and flesh-eating reptiles, and some of these were even mere ugly than their Morrison progenitors. Ankylosaurus was an armored dinosaur whose entire back was covered by flattened ridged-skin plates of bone. The animal was low of stature, had a short, blunt head, and carried on the end of its stout, heavy tail a great triangular club of bone. Even the eyes were provided with a cup-shaped bony shutter, like the visor of a helmet, which could be closed over the eyeball, so that all the vulnerable parts of this animated fortress were protected by bony armor. The "horned toad," one of the small modern lizards of the western plains, is not very different from the armored dinosaurs except in size. (See Pl. XI, A, p. 53.)

The most striking of the flesh-eating dinosaurs was the Tyrannosaurus, or tyrant lizard, the largest carnivorous animal that ever lived on land. It was 40 feet in length, and when it stood erect the top of its head was 18 to 20 feet above the ground. The fore limbs were small, and it must have walked entirely upon its powerful hind legs. A perfect skull of this animal is exhibited in the American Museum of Natural History in New York City. The jaws are 4 feet in length and bristle with sharp-pointed teeth, several of which project 6 inches from their sockets. It is with a feeling of awe that one standing before the huge head contemplates a beast of such terrible ferocity.

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East of Percy the train enters a cut 65 feet deep and 1-1/2 miles long through beds of coal, carbonaceous shale, and sandstone. It is reported that the coal taken up here by the steam shovel was used in the engine and furnished the power for making the cut. The best bed thus exposed contains coal 8 feet thick.

Elk Mountain, which is visible from many points on the route, is seen to best advantage to the left (south) from Percy station. This great mountain of granite, conical in form and 7 miles in diameter at its base (Pl. XII, B), rises to an altitude of 11,162 feet and is at the north extremity of the Medicine Bow Range. To the west of it is a relatively small peak of irregular outline called Sheephead Mountain. Farther southwest can be distinguished on a clear day the Sierra Madre, near the northern boundary of Colorado.

PLATE XII.—A (top), PLATTE RIVER AT FORT STEELE, WYO. A characteristic view of the Cretaceous rocks in central Wyoming. B (bottom), ELK MOUNTAIN, THE NORTH END OF THE MEDICINE BOW RANGE. This mountain may be seen during nearly 150 miles of the journey over the Union Pacific Railroad. Photograph furnished by Union Pacific Railroad Co.

About 1-1/2 miles west of Dana the traveler passes from the rocks of the "Upper Laramie" to those of the underlying "Lower Laramie" formation, but the change is inconspicuous from the train because the rocks are obscured by surface material near the road. The "Lower Laramie" consists of sedimentary rocks more than 6,000 feet thick, mainly coarse-grained sandstone, in which are a few thin beds of coal. These rocks contain fossil plants and shells of fresh-water mollusks, although brackish-water and marine fossils occur near their base.

Between Dana and Walcott the strata are bent up in one of the great arches or anticlines of this much-disturbed region. Edson is on the Lewis shale, but the beds of the North Park formation (Tertiary) extend to the railroad from the south. A mile farther southwest, beyond a short tunnel, is a deep cut through the crest of the St. Mary anticline, which consists of the arched sandstone of the Mesaverde formation. The crest of the ridge is formed of this sandstone, which is harder and has therefore resisted erosion better than the shaly beds that originally covered it.

South of the tunnel the train again crosses the Lewis shale and the "Lower Laramie" formation before it reaches Walcott. The town of Walcott is built on the North Park formation, which here covers the older strata. This formation takes its name from North Park, Colo., where it occupies an extensive area and contains thick beds of coal. From Walcott a branch road runs south to Saratoga and Encampment. Saratoga is on Platte River and is well known to sportsmen for its hunting and fishing. Here are some hot sulphur springs and a well that furnishes a mineral water sold under a distinctive name. Encampment, 43 miles south of Walcott, at the end of the branch line, is the center of a copper-mining district which formerly produced considerable ore but is not now very active. This district is in the Sierra Madre. Copper was discovered here in 1868, but not until 1881 did the district become productive. Altogether it has yielded over 20,000,000 pounds of copper. Gold, silver, and other metals have been found in small quantities. The mines are in crystalline and metamorphic rocks, of pre-Cambrian age, cut by intrusive rocks, including gabbro, which is supposed to he the source of the copper ore.

About 2 miles due north of Walcott is a prominent hill known as St. Mary Peak, which rises 7,496 feet above sea level. This peak and the ridge extending northwestward from it are composed of upfolded beds of the Mesaverde formation. The strata, during the process of folding, were broken and thrust upon one another in such a way that those east of the fracture were pushed up over those west of it, so that certain beds of the Mesaverde formation now rest upon younger beds that were originally laid down on top of that formation.

Two miles west of Walcott the railroad leaves the nearly horizontal beds of the North Park formation and reaches the steeply inclined massive yellow sandstones of the Mesaverde formation, which are carved by erosion into a great variety of forms. These sandstones make a conspicuous ridge that extends northwestward for many miles. The part of the ridge between Walcott and the point where North Platte River crosses the formation is known as the Rattlesnake Hills; the part north of the river is called the Haystack Hills.

Three miles east of Fort Steele the railroad leaves the Mesaverde beds and reaches a formation which has been named the Steele shale,¹ from its occurrence here. This shale is the same as that which crops out near Medicine Bow and extends westward from that place beneath the coal-bearing rocks of the Hanna Basin.

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¹The upper part of the Steele shale is much more sandy near Fort Steele than it is farther east, and several prominent sandstones lie below the massive sandstone that is here mapped as the base of the Mesaverde.

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The town of Fort Steele derives its name from Fort Fred Steele, an army post established here in 1866 to guard the Union Pacific Railroad against Indians. At the time of the Meeker massacre, in the early eighties, it was from Fort Fred Steele that the unfortunate force commanded by Maj. Thornburg was sent to put down the uprising. Maj. Thornburg and most of his command never returned. That any of them survived was due to the dispatch of a second expedition from the fort to their relief. There is little about the town now to suggest the troublous Indian times. It serves as a place of supply for sheep herders and for the farms scattered up and down North Platte River wherever the valley is wide enough to be cultivated. The North Platte, from which the railroad diverged at the city of North Platte, 291 miles west of Omaha, is reached again at Fort Steele, 384 miles west of North Platte and 3,705 feet higher.

From its source in North Park, Colo., the North Platte follows a circuitous route to the north until it reaches a point nearly halfway across the State of Wyoming. In this part of its course it cuts through the Seminoe Mountains and passes completely around the north end of the Laramie Range. In the Seminoe Mountains the river has cut some remarkably picturesque gorges. Across one of these the United States Reclamation Service built the Pathfinder dam, 218 feet high, creating a reservoir having a capacity of 1,100,000 acre-feet—that is, enough water to cover that number of acres to a depth of 1 foot. In this reservoir flood waters that formerly went to waste are stored, to be released as needed to irrigate 130,000 acres in eastern Wyoming and western Nebraska. This project, which is not yet completed, will cost nearly $7,000,000.

To the left (south) as the train crosses the bridge over the North Platte at Fort Steele may be seen a sawmill which works timber cut in the mountains and floated down the river. This mill produces many railroad ties and mine props from timber grown in the Medicine Bow and Hayden national forests.

North of Fort Steele the Rattlesnake Hills rise from the river level by a series of escarpments, and about 2-1/2 miles south of the town there is another series of escarpments, composed also of the Mesaverde formation and the sandstones of the transition beds between the Steele shale and the Mesaverde, which are illustrated in Plate XII, A. If the traveler were to make an excursion to these two ridges he would observe that the strata in the Rattlesnake Hills dip toward the northeast, whereas those in the ridge south of Fort Steele dip toward the south. If the strata of these two ridges were projected upward along their dip till they met, they would form an arch whose crest would be a little south of Fort Steele. As a matter of fact the Mesaverde formation did at one time extend over such an arch. When these beds were bent up by the development of the fold they were probably fractured at its crest. Along this line of fracture the hard sandstones were more easily eroded than elsewhere and were finally cut through by the streams. The underlying soft shale was then rapidly eroded along the crest of the fold, so that in time the axis of the arch, which was originally a ridge, was reduced to a valley bordered on either side by flaring walls of sandstone. This valley, now several miles wide, is followed by the railroad from Fort Steele to Rawlins.