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

SHEET No. 15. (click on image for an enlargement in a new window)

Morgan is the center of a rich agricultural district that is especially noted for the fine quality of the peas which are raised here. From Morgan (see sheet 15, p. 102) about 90 carloads of canned peas are shipped each year. The broad valley which makes this industry possible is due to the presence of soft rocks, in which the river has greatly widened its valley while it was cutting the narrow gorges in the hard rocks both east and west. These rocks once filled a basin lying between the two ranges of the Wasatch Mountains. East of Morgan rise the craggy slopes of the Bear River Range, though which the train has just passed, and which attains an altitude of 9,245 feet in Mount Morgan, north of the town. To the west may be seen the rugged crest of the main range of the Wasatch Mountains, which in this latitude consist entirely of granitic rocks of Archean age—that is, rocks which are older than the oldest sedimentary rocks that contain remains of plants or animals. (See table on p. 2.)

Just before entering Morgan the train passes close to the foot of a slope on the right (north) in which dark-colored limestone containing fossil corals and shells of early Carboniferous (Mississippian) age is well exposed. Farther west rocks of Ordovician and Cambrian age are exposed north of the track, but these can not be readily distinguished from the train.

The soft Tertiary rocks that occupy the basin west of Morgan may be seen to the right from the train, north of Peterson, where they appear as light-green to pink strata, slightly conglomeratic and inclined toward the east.

The station at Peterson is near the center of the basin just described. The basin was formerly occupied by a bay of the ancient Lake Bonneville, whose waters backed up through Weber Canyon. (See pp. 97-99.) Along the margin of this bay, which was 300 feet or more in depth, sand and gravel accumulated in large quantities. When the water withdrew from the basin these beach accumulations were left as a shelf, remnants of which lie about 300 feet above the railroad at many places on the slopes.

Many a "station" along the Union Pacific Railroad consists of nothing more than a signpost, but at Strawberry not even a post is visible. It is a switch for sidetracking cars to gravel pits, which may be seen to the right, north of the railroad, and which furnish gravel for ballast. From many places near Strawberry the traveler may get good views of Mount Morgan, to the east, and of Observation Peak (over 10,000 feet above sea level), which lies to the north (right) and is here the most prominent mountain north of the railroad. To the left (south) rises the main mass of the southern part of the Wasatch Range.¹

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¹The Wasatch is the easternmost of the basin ranges. Although very complex in structure, it may be described briefly as a great block of the earth's crust that has been elevated at its western margin, so that it inclines eastward. Its tilting was made possible by a break of the crust in a north-south direction along what is now the western base of the range. The rocks that lie east of this line of fracture were pushed up many thousands of feet higher than those that lie west of the line, thus producing a great fault. Later the elevated part of the block was eroded, so that now its surface is a complicated mass of rugged mountains, separated from one another by valleys, canyons, and gorges.

The western face of the range which was originally nearly straight and might have been a single cliff had it not been eroded, is still very precipitous and forms what is known as a great fault scarp. It is this western fault scarp that is so impressive as seen from Ogden and other points in the valley of Great Salt Lake.

The Uinta Mountains differ from the Wasatch Mountains in that they have resulted from the erosion of a broad arch whose axis trends east, nearly at right angles to the Wasatch axis. The Uinta is the westernmost of the Rocky Mountain ranges, which reach their maximum development farther east in central Colorado. The junction of this range with the Wasatch constitutes the transition between the Rocky Mountain ranges—modified arches whose axes have a northerly trend with a marked tendency toward westward deflection—and the Basin Ranges—tilted blocks, whose axes have a regular northerly trend.

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Just before reaching Gateway station the route passes abruptly from the open valley into the narrow V-shaped gorge cut by Weber River through this great range of mountains. Precipitous, craggy slopes rise on both sides and the scenery is varied and impressive. The river descends rapidly in this canyon and the power furnished by it is utilized by hydroelectric plants. Soon after entering the canyon the train passes to the left (south) of a diversion dam at which a large part of the water is turned into a pressure pipe 6 feet in diameter. From this pipe it emerges about 2 miles downstream, at an altitude 172 feet below the intake, at the power house of the Utah Light & Railway Co., from which 5,000 horsepower is transmitted 35 miles to Salt Lake City. From the power house the water is carried by a canal along the south wall of the canyon to the turbines of a second power house, from which it is distributed for irrigating the lands of the valley below. The once worthless desert has thus been transformed to green fields and fruitful orchards which support a thriving community.

Toward the lower end of the canyon the river makes a sharp turn to the right through a rocky defile called Devils Gate. Instead of passing through this defile, the railroad is built through a cut made in unconsolidated gravel which fills a former channel of the river. Apparently this old channel was filled during one of the stages of high water in Lake Bonneville (see pp. 97-99), and when the lake water withdrew the river was deflected to the right at this point and cut a new channel in the solid rock, making what the physiographer calls a young channel due to superimposed drainage.¹

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¹The behavior of the river at this point gives the key to an understanding of its course across the Wasatch Range. The river rises east of this range, but instead of taking the seemingly easier course around the mountains, as Bear River did, it has cut its way directly through them. West of Echo it leaves the open basin-like valley and enters a narrow gorge nearly 2,000 feet deep. West of Devils Slide it enters a canyon cut to a depth of 4,000 feet or more through the Bear River Range. West of this range it crosses another open space and once more enters a narrow canyon within which it passes through the main range of the Wasatch Mountains.

In Tertiary time such valleys as may then have existed in this region were filled with gravel, sand, and silt, and practically the whole region was aggraded or built up to nearly a common level. Over this plain the streams established their courses without regard to the kind of rock beneath the surface. Weber River chose the course of least resistance at that time, and when it deepened its channel and found itself flowing directly across the ridges of hard rock that now form the Wasatch Mountains it was too late to change. The energy of the stream has been sufficient to cut only narrow gorges in the hard rock, but in the softer rock it has excavated the broad valleys west of Echo and near Morgan.

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On emerging from Weber Canyon the train crosses the line of the great fault by which the rocks on the east were uplifted many thousands of feet relative to those on the west. Here we enter a broad, fertile valley that is well watered by the river. If the traveler covered with alkali dust from the deserts farther east reaches this valley when the orchard trees are bending to the ground under their burden of ripening fruit he will not wonder that some of the inhabitants call it "Zion."

This valley has been eroded from a broad delta of gravel, sand, and silt built up by the river during the Pleistocene epoch, when the waters of Lake Bonneville covered the region. The form of the delta is not visible from the train, because the railroad follows the trench that the river subsequently cut in the old delta. The accompanying map (sheet 15, p. 102) shows that a gently sloping surface with Ogden near its center extends from Farmington nearly to Brigham, a distance of 30 miles, and from the foot of the mountains westward to the lake, a distance of 17 miles. This is the delta built by Weber and Ogden rivers and several smaller streams.

Two prominent beach lines are plainly visible on either side of the canyon. The higher one, known as the Bonneville terrace, is nearly 1,000 feet above the river and marks the level reached by the water when the lake was at its maximum height. The lower one, known as the Provo terrace, is 375 feet below the Bonneville terrace and denotes a later stage of the lake. From points at a considerable distance these so-called "waterlines," some made by deposits of gravel and others by notches cut by the waves of Lake Bonneville in the hard rock, may be seen all along the western face of the mountains. (For a description of these terraces and the phenomena associated with them see pp. 97-99.)

The valley of Weber River, which appears so attractive in the vicinity of Uinta, is a small part of the Great Salt Lake valley, which includes a large part of northern Utah. This is the home land of the Mormons, and according to the historian Hubert H. Bancroft it is "a new Holy Land, with its Desert and its Dead Sea, its River Jordan, Mount of Olives, and Galilee Lake, and a hundred features of its prototype of Asia."

Ogden is the western terminus of the Union Pacific system. Through passengers on the Overland Route here pass without change of cars to the Southern Pacific line which connects Ogden with San Francisco. Passengers for Yellowstone Park change to the Oregon Short Line, and those for Salt Lake City¹ have the choice of the Salt Lake & Ogden electric road, the Oregon Short Line, or the Denver & Rio Grande. The railroad time changes here from mountain to Pacific time, and the westbound traveler should set his watch back one hour.

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¹Salt Lake City, 37 miles south of Ogden, is the capital of Utah and the seat of government of the "Church of Jesus Christ of Latter-Day Saints," whose adherents are commonly called Mormons. It is a city of 92,777 inhabitants, beautifully situated between the shore of Great Salt Lake and the lofty and precipitous front of the Wasatch Mountains. Many of the natural features are unique, especially the great lake of brine so salty that no fish can live in it and so dense that the bather floats on it like a cork on ordinary water. But this city is of interest mainly as the headquarters of the Mormon Church, which has grown so rapidly that in place of the 40 who organized it in 1830 it now has a membership of about 500,000. Here are the Temple, the Tabernacle, and many other objects of interest. The city was founded in 1847 by the first company of Mormon emigrants under Brigham Young and was the point to which later companies came and from which they went out to possess the land. The story of this migration and the establishment of the new sect in the wilderness is of absorbing interest. The fortitude with which these people endured hardships and suffering and their unwavering devotion to a fixed purpose compel admiration.

Bingham Canyon, the principal copper district of Utah, is easily reached from Salt Lake City. The ores occur mainly in limestone of Carboniferous age and in an intrusive igneous rock (monzonite porphyry) which cuts the limestone. The low-grade disseminated ores in porphyry are now more important than the ores in the limestone. In 1913 the disseminated ore mined, chiefly by steam shovels, amounted to 8,300,000 tons, yielding about 0.75 per cent of copper and some gold and silver.

The Park City and Tintic districts, which produce large quantities of ores carrying chiefly lead and silver, can also be visited from Salt Lake City.

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Ogden is the county seat of Weber County and the second largest city in Utah. It is said to have been named for an old trapper and was laid out under the direction of Brigham Young in 1850. Ogden has a variety of industries, owing in part to its good transportation facilities and cheap electric power. Canning is one of the most important. In 1913 canneries adjacent to the city made an output of nearly a million cases (approximately 24,000,000 quarts) of fruit and vegetables, of which more than half was tomatoes.

Ogden lies at the foot of the Wasatch Mountains, which rise abruptly just east of it, and is on the border of the flat floor of Great Salt Lake valley, stretching away to the west. The business part of the city is on one of the later terraces cut by the waves of the ancient Lake Bonneville, described below by G. K. Gilbert,¹ in an apron of mountain waste; the main residence section rises eastward to the level of the Provo terrace, which was built by this lake when its surface remained for a long time at an elevation about 625 feet higher than the present lake.

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¹At Ogden the traveler is fairly within the Great Basin, and for 590 miles, until he reaches the crest of the Sierra Nevada, his course traverses a series of closed valleys—valleys which resemble basins in the fact that all parts of their rims stand higher than their middle parts. All streams of this region either lose their water by direct evaporation or discharge to some lake that serves as an evaporation pan. Some of the lakes have outlets, but every such outflowing stream flows into another lake, and the final receptacle has no outlet, all the water it receives escaping upward, into the air. No stream in the Great Basin finds its way to the ocean.

Great Salt Lake has no outlet. Jordan River, which enters it from the south, is the outlet of Utah Lake. Bear River, coming from the north, carries the outflow from Bear Lake. The waters of Utah and Bear lakes and of Jordan and Bear rivers are fresh, and so is the water of Weber River, the third great tributary of Great Salt Lake, but the lake into which the three rivers flow is saline. It is saline because it has no outlet. The fresh waters of the rivers contain some saline matter, but the quantity is too small to be discovered by taste. As stated by the chemist, in parts per million, the quantity seems minute, but when account is taken also of the total volume of water brought by the streams to the lake in a year their burden of saline matter is found to be really great, annually to more than 500,000 tons. Year by year and century by century the water which they pour into the lake is evaporated, but the dissolved solids can not escape in that way and therefore remain. They have accumulated until the lake water is approximately saturated, holding nearly as much mineral matter as it can retain in solution. The lake contains over 5,000 million tons of common salt and 900 million tons of Glauber's salt, or sodium sulphate, as well as other mineral matter.

Another consequence of the lack of outlet is that the lake varies from time to time in size. Whenever the gain from inflow is greater than the loss from evaporation the level of the water surface rises; when the loss is greater it falls. Each year there is a rise, beginning in winter, when the cool air has little power to absorb moisture, and continuing it through spring, when the rivers are swollen by the melting of snows in the mountains. Each year there is a fall, beginning in summer, when the hot air rapidly absorbs the water, and continuing in autumn, when the rivers are smallest. This annual oscillation amounts on the average to about 16 inches.

In some years the rainfall and snowfall are greater than in others, and then the lake usually receives more water than it parts with, so that the surface is left higher than it was before. In a series of wet years the lake level progressively rises; in a series of dry years it progressively falls; and as the rainfall is irregular the fluctuations of the lake are conspicuous. Since definite knowledge of the lake began, in 1850, there have been five periods of increase and four of decrease. (See fig. 11.) The summer levels of 1868 and 1877 were more than 10 feet above the summer level of 1850, and those of 1903 and 1905 were 4 feet below that of 1850. The level of 1914 was 6 feet above that for 1905.

FIGURE 11.—Diagram showing fluctations of water surface of Great Salt Lake, Utah, from 1850 to 1914. (click on image for an enlargement in a new window)

The land bordering the lake has in many places a slope so gentle that a amounting small change in the height of the water surface makes a great change in the area of the lake. On a map completed in 1850 the area shown is 1,750 square miles; on a map made in 1869 it is 2,170 square miles. In the interval between the two surveys the lake had risen 10 feet, and this rise enlarged the area about 24 per cent. From the greater surface the evaporation was of course greater, and the dependence of evaporation on area is thus an important factor in regulating the size of the lake. The effect of a long series of wet years is somewhat reduced by the resulting increase of evaporation surface, and the effect of a series of dry years is lessened by the resulting reduction of surface exposed to evaporation. This natural and automatic control limits the range of oscillation and gives a certain permanence to what may be called a normal or average level. A change in the normal can occur only when some new factor is introduced.

Both man and nature have introduced new factors and thus have produced changes in the normal level. The occupation of the surrounding region by white men has recently modified the face of the land in ways that have a recognized influence on the water level; and the ancient history of the lake includes enormous modifications in response to changes of climate.

Of human influences the most telling has arisen from the development of agriculture with irrigation. In irrigation the water of rivers and creeks is diverted to cultivated fields, which first absorb it and then through evaporation feed it to the air; and the water thus consumed by utilization is lost to the lake. With the gradual enlargement of the irrigated area the normal level of the lake is inevitably being lowered, and engineers are already confident that the high-water mark of 1877 will never again be reached. On the other hand, there is no reason to expect the lake's extinction, for there is a limit to the possibilities of irrigation.

The fresh water brought by the rivers mingles gradually with the brine, and as the river mouths are on or near the eastern shore, the brine is not so strong at the east as at the west. Analyses from samples of the brine gathered at different points and in different years report the dissolved solids as from 13.7 to 27.7 per cent, by weight. A sample taken in August, 1914, contained 18.9 per cent of solids. At the present time the average salinity of the lake is about 5-1/2 times that of the ocean, and its density is 14.5 per cent greater than that of fresh water. Only with difficulty can the bather keep his feet from rising to the surface, and if he balances himself in an upright position his head and shoulders are above the surface.

The brine is weakest in the northeastern arm, the portion visible from the train near Brigham. This arm has been partitioned from the main body by the embankment of the Southern Pacific Co. and is continuously supplied with fresh water by Bear River. Ice can form on the stronger brine only in zero weather, but this arm is frozen from side to side every winter and sleighs have been driven across it.

The only climatic element with which the lake oscillations have been connected by direct observation is precipitation—the lake rises or sinks as the fall of rain and snow is great or small—but it is easy to understand that the balance between supply and loss of water may also be disturbed by any change of climate which affects the rate of evaporation. As every laundress well knows, evaporation is favored by heat, by dryness of the air, and by strength of wind and is retarded by cold, by moisture in the air, and by calm. So there are at least four ways in which changes of climate may cause the lake to expand or contract. The latest of the periods into which geologists divide past time witnessed a series of climatic changes which affected the whole earth, and though all the elements just mentioned were doubtless involved, the element which recorded its changes most clearly was temperature. There were several epochs of cold, and they were separated by epochs of warmth. During the cold epochs the high parts of the Wasatch Range held a system of glaciers, and in one of them several ice tongues protruded so far beyond the mouths of the mountain canyons that they heaped their moraines on the floor of Jordan Valley, only a few miles from the place where Salt Lake City now stands. In that epoch of cold the rate of evaporation was far slower than now, and evaporation was at so great a disadvantage in its contest with precipitation that there was immense expansion of the water surface. When the lake was largest it was comparable in area and depth with Lake Michigan; it had eleven times its present extent. In attaining this great expanse the water surface rose to a position more than 1,000 feet above its present level.

To this great body of water geologists apply a distinctive name, Lake Bonneville, and they have given much attention to its history, which is written in shore lines, deltas, channels, deposits, and fossils. The shore lines appeal most to the traveler, and may be seen from car windows at several points.

As a matter of definition a shore is merely the meeting place of land and sea or of land and lake, but as a matter of land form it is much more. At the shore the lashing of storm waves works changes in the land, giving it new shapes. At some places the land is carved away; at others it is made to encroach on the water. Where it is eroded the limit of erosion is marked by a cliff, and below the water is a shelf of gentle slope. Where additions are made they take the form of beaches or bars, which rise little above the water level and are composed of sand or gravel. At some places a bar spans a bay from side to side; elsewhere it is incomplete, projecting from a headland as a spit.

The waves of Lake Bonneville were as powerful as those of Lake Michigan and fashioned the shore into an elaborate system of cliffs, beaches, and spits; and when the waters finally fell to lower levels they left behind the shapes their waves had made. The base of each surviving shore cliff is a horizontal line, and so is the crest of each beach, bar, and spit, and these features in combination trace the outline of the old lake as a level contour about the sides of the basin and the faces of mountains that were once islands in the lake.

In rising and falling the waters lingered at many levels, and so there are many ancient shore lines, but two of them are more conspicuous than the rest and have been named. The highest of all is the Bonneville shore line, and 375 feet lower lies the Provo shore line. The Bonneville line represents a relatively short stand of the water and is conspicuous chiefly because it marks the boundary of wave action. All the slopes below it have been more or less modified by the waves, but the slopes above it retain the shapes which had been given them by other agencies. The Provo line represents a long stand of the water and is conspicuous because it is strongly sculptured.

In all the early history of the great lake its basin was closed, like that of the modern lake. The water surface rose and fell in response to climatic changes, like that of its modern remnant. The last great rising was the highest and terminated the series of oscillations by creating an outlet. The lowest point of the basin's rim was at Red Rock Pass (90 miles by rail north of Ogden), and when the water rose above that level the stream which began to cross the pass descended to Portneuf River, a tributary to Snake River, the chief branch of the Columbia. Through the creation of this outlet the Bonneville Basin, which had previously contained an independent interior drainage system, became part of the drainage system of the Pacific Ocean.

Red Rock Pass was not a mountain pass, a notch in a rocky crest; it was merely the highest point on the axis of a valley between two mountain ranges. Valley and ranges ran north and south and the valley was floored by alluvium washed from the ranges. From the Red Rock summit the valley sloped gently northward toward the Portneuf and southward toward Bear River. The formation at the summit consisted of soft earth, and as soon as overflow began a channel was formed. The deepening of the channel increased the volume of the stream by lowering the outlet of the lake, the greater stream was more efficient in deepening the channel, and these two causes interacted until the stream became a stupendous torrent. The volume of water discharged before the flow became steady was enough to supply Niagara River for 25 years, but the record of the torrent's violence leads to the belief that it lasted for a much shorter period.

The rapid deepening of the outlet channel was finally checked when the stream reached a sill of solid rock beneath the soft alluvium of the pass, and upon this sill the outlet rested for a long period. The lake surface then no longer oscillated in response to varying climate but held a constant level, and it was the long maintenance of this level which enabled the waves to carve and construct the Provo shore line.

The draining of the lake down to the Provo level reduced its area by one-third and correspondingly reduced the quantity of water annually evaporated. Two-thirds of the inflowing water was then disposed of by evaporation and the remainder was discharged through the outlet. Only a great change of climate could restore the balance between inflow and evaporation, and the change was slow in completion. At last, however, the pendulum of temperature swung far enough on the side of warmth. The outlet channel ran dry, the lake basin was again separated from the drainage system of the Pacific, and the lake began to shrink. So long as there was outflow the water was fresh, but when the outflow ceased there began that accumulation of salt which has made the water of the present lake a concentrated brine.

At times in the history of the lake, especially while the Provo shore line was being formed, the tributary streams brought down sand and gravel, which they dropped at their mouths, building deltas. When the water fell these deposits remained as fan-shaped benches having steep fronts. The streams that built them then dug channels through them. Part of the city of Ogden stands on a delta bench built by Ogden River. Between Weber Canyon and Ogden the railroad follows the channel that was opened by Weber River through its former delta.

The climatic revolutions which created and destroyed Lake Bonneville wrought similar changes in all parts of the Great Basin. In Western Nevada the traveler sees the shore lines of another ancient lake, known to geologists as Lake Lahontan. It did not rise high enough to establish an outlet, but its water was so nearly pure as to be inhabited by fresh water shells. Some of its shores are marked by heavy deposits of travertine. When it died away there remained in its basin a group of smaller lakes, some salt and some fresh, but only one—Humboldt, a fresh lake—can be seen from the train.

The view from Ogden station is obstructed by buildings and trees, but by climbing to a near-by viaduct one may see the bold face of the Wasatch Range, across which the line of the Bonneville shore is drawn as a narrow pale band. On the shore bench grow the ash-green sage and other light-colored bushes, and the steeper slopes are mottled by dark-green thickets of dwarf oak. The westbound traveler obtains a better view by looking backward just after leaving Ogden, and may probably recognize the Provo shore line as well as the Bonneville. These traces of old shores appear on Promontory Range and Fremont Island; and if the air is clear the traveler will have the old shore lines in view until he leaves the Bonneville Basin near Montello, 130 miles from Ogden.

On the route from Ogden to the Yellowstone National Park the old shore lines are prominently and almost continuously in sight until the train enters Bear River Canyon and may also be seen on a distant range to the left. They reappear in Cache Valley, beyond this canyon, and are especially conspicuous at the left where their terraces surround a range of hills. At the Provo stage of the lake these hills projected above the water as a long island, and at the Bonneville stage as a chain of smaller islands. Between Oxford and Downey the railroad traverses the Red Rock outlet channel, one of the stations, Swan Lake, being within the channel. The modern streamlets, flowing from neighboring hills, have brought down enough gravel and sand to build alluvial dams and have thus obstructed the drainage of the old river bed, so that it now contains a series of ponds and marshes.

In quality of water and in temperature Lake Bonneville was as well fitted for abundant and varied life as the Bear Lake of to-day, and though the only remains yet found in its sediments are fresh-water shells, we need not doubt that its waters teemed with fish. We may confidently picture its bordering marshes as fields of verdure and its bolder shores as forest clad; and we may less confidently imagine primitive man as a denizen of its shores and an eyewitness of the spectacular deluge when its earthen barrier was burst.

The only permanent animal inhabitant of Great Salt Lake is a tiny "brine shrimp," a third of an inch in length. A more conspicuous temporary resident is a minute fly which passes its larval stage in the water, and when its transformation takes place leaves behind it the discarded skin. These flies are so numerous in their season that even the passing tourist should feel grateful that they do not bite. Their brown exuviae darken the water edge and often sully broad belts of the lake surface. More decorative denizens are gulls and pelicans, which find safe nesting ground on some of the smaller islands. There are no shoal-water plants, and the salt spray of the beach is fatal to all land vegetation along the shores.

When the lake is low its salt is segregated and deposited in shallow lagoons at its margin, to be redissolved when the water rises. Each autumn, as the water cools, deposits of hydrated sodium sulphate (Glauber's salt) coat piles and other fixed objects near the water surface, and the deposits increase as the temperature falls. In the depth of winter large masses of this salt may be seen along the embankments and trestles of the Lucin cut-off. Calcium carbonate, the mineral constituting limestone, travertine, and chalk, is continuously and permanently separated from the water, which is unable to retain that which is brought to it by the rivers. Along the shores it forms minute balls, which together constitute sand, a sand quite distinct from the siliceous sand of ordinary beaches.

Man makes little use of the lake. On its shores there are neither fisheries nor ports, and commerce finds it an impediment rather than an aid. Its deposits of Glauber's salt, which it offers for the gathering, are neglected because the world's demand is small and is cheaply met in other ways. Its common salt is harvested with great economy of effort, for impurities are easily excluded and the work of evaporation is performed by the sun. The present annual output of 40,000 tons must be multiplied fivefold before it can commence to weaken the brine. For the rest man is content to resort to its shore for bathing and to realize a new sensation as he floats upon its surface.

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From the station at Ogden may be seen Observation Peak, 6 miles to the east, its top over 10,000 feet above sea level and more than a mile above the railroad. This is the culminating peak of the Wasatch Mountains (Pl. XXVIII, p. 104), a range that came into existence in comparatively recent geologic time and that has an interesting origin.¹

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¹Most of the rocks in the Wasatch Range were laid down as sand and mud on the bottom of the ancient sea, where they became compacted and hardened into sandstone, shale, and limestone. The sea bottom eventually became land. As mother earth has aged her skin has cracked and wrinkled. In the Utah-Nevada region many long cracks were formed and the rocks on one side or the other were moved slowly upward or downward, forming long ridges along the cracks, steep on one side and gently sloping on the other. Such breaks in the earth's crust are called faults. A fault may be a few feet or hundreds of miles long, and the distance which the rock beds on one side slip past those on the other may range from a fraction of an inch to thousands of feet. When the rocks on one side are shoved up over those on the other side the break is called a reverse or overthrust fault. (See fig. 12.)

FIGURE 12.—Diagram showing normal faults (a) and a reverse or overthrust fault (b).

In the region now occupied by the Wasatch Mountains a number of parallel faults were developed close together and the broken pieces of the earth's crust between them were pushed up, the rocks on one side of each crack riding up over those on the other side until a great mountain range was formed where once lay a plain. The accompanying diagram (fig. 13) illustrates the structure of the Wasatch Range in cross section. During the long period of slow earth movement which made these mountains flat-lying parallel beds of rock were locally turned on edge, crumpled, and folded in a wonderfully intricate manner. These upturned and crumpled rocks are well exposed in Ogden Canyon. The west face of the Wasatch Range is believed to mark the plane of a normal fault (fig. 12) at a nearly vertical crack in the earth's crust, the rocks on the east side of which went up or those on the west side went down. The forces which have raised these mountains are still active, for movement along this fault has disturbed the surface recently.

FIGURE 13.—Diagrammatic structure section of the Wasatch Range in Ogden canyon.

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[For continuation of itinerary to San Francisco, see p. 148.]

To see the structure of the Wasatch Mountains, the traveler should make a side trip to the local scenic attraction, Ogden Canyon, which can be reached by street car from Ogden station. In Ogden Canyon, bright afternoon sunlight it can easily be seen that the face of the range is divided into bands of different rock formations. (See Pl. XXVIII, B, p. 104.) Observation Peak itself is a mass of pink rock called quartzite. This rock was a widespread bed of sand which was laid down on the bottom of the sea about the time the earliest forms of life appeared on the earth. How it reached its present position has been explained in the preceding footnote. A dark band of rocks, partly concealed by brush and timber, lies below the peak. In a spur much lower down the mountain is another band of pink quartzite which makes a 1,000-foot wall and rests on a dark band similar to the one above it. This pink rock is a part of the same formation as that at the peak, the repetition being due to breaking of the earth's crust and piling up of the fragments. In fact the structure of the mountains at Ogden is not unlike that of the cakes of ice in an ice jam.

Just before reaching the mouth of the canyon the traveler may see a nearly perpendicular bluff or scarp, a few feet high, at the top of the bank above a gully a few rods southeast of a single-arch concrete bridge. This small bluff, which was made by recent uplift along a great fault that parallels the mountain front, is best seen from the higher bench land. (See Pl. XXVI, B.)

PLATE XXVI.—A (top), Z-SHAPED FOLDS NEAR EAST END OF OGDEN CANYON. The lines follow the outcrops of the folded beds. B (bottom), RECENT FAULT SCARP AT THE MOUTH OF OGDEN CANYON. Scarp is dark wavy line crossing the meadow.

The steep face of the mountain range represents the exposed edges of geologic formations whose continuation west of the fault is now far below the level of the plain. The mouth of the canyon is in very old, greatly distorted rocks (Archean gneiss and schist) which were formed before life began on the globe. Warm springs issue near the bridge below the month of the canyon, and where the trolley road passes over a steel bridge just inside the canyon a warm spring in the south bank of the river steams forth from the contact between pink quartzite and somber-colored gneiss. The water is salty, contains iron, and has a temperature of about 136° Fahrenheit. Rounding a curve brings into view a waterfall which shoots out from the rocks several hundred feet above the track and turns to spray. The water collects on the rocks below and cascades into the river. This is an artificial fall, made by a hole in a flume that carries water to a hydroelectric plant. Close to the foot of this fall the bedrock wall of the canyon is plastered by a deposit of thoroughly cemented gravel, a remnant of the material that choked the canyon when. Lake Bonneville backed up into it.¹

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¹G. K. Gilbert describes this material as follows:

"The lower part of the canyon through its length, but especially near its mouth, is more or less lined with heavy beds of coarse gravel, thoroughly consolidated by a ferruginous cement. In some places this forms the bed as well as the banks of the stream; but at others it is cut through, and the original well-worn rock bottom of the old channel is exposed beneath the gravel by the side of the road. It is evident that when this canyon was originally excavated the Great Salt Lake was not far if at all above its present level; so that the rushing torrent which wore out this old rounded bottom met no check until it had passed entirely beyond the mouth of the canyon. There followed a time when the lake filled nearly or quite to its highest terrace; and meanwhile the Ogden River continued to bring down the sand and pebbles which it had before been accustomed to sweep out upon the lower terrace, but now, checked by the rising lake, deposited them in the lower parts of its old channel, until they accumulated to a very high level, not yet accurately located. Again the lake retired and the stream again cut down its channel, sometimes reaching its old level and sometimes not."

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The canyon at this point is very narrow, and there is barely room for the highway on one side and the trolley-car tracks on the other side of the river (Pl. XXVII). The mountain walls that rise thousands of feet above appear almost insurmountable, and directly ahead they seem to completely block further passage upstream. But a little turn shows a thin notch cut by the river through a great mass of quartzite beds standing nearly on edge. This is the same pink formation as that in Observation Peak, and its presence and position here show how much these rocks have been turned from their original flat-lying position. The nearly vertical slitting or gashing of the rocks is merely the result of weathering between the original beds of sand as laid down on the sea bottom. The passage is narrow because of the great hardness of the rocks, for the whole valley, like most other valleys, has been made by the gradual washing away of material by its stream and is narrowest where the rocks are hardest. Above the narrows the valley walls are limestone and shale, which are more easily worn away than the quartzite. A limestone quarry and kilns are situated just above the narrows on the south side of the river.

PLATE XXVII.—VIEW IN OGDEN CANYON BELOW THE NARROWS. Looking upstream to gap cut in Cambrian quartzite.

Farther up Ogden River (which, by the way, would be called a brook or run in some parts of the country) city people have built summer homes along the stream bank.

In 1914 the trolley line ended 7 miles from Ogden at The Hermitage, a rustic hotel built of logs and stone. The verandas of this hotel afford a vantage point for enjoying the rugged canyon scenery.¹

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¹Ogden Canyon was cut in the solid rock by the river which now flows through it. Running water carrying sand and gravel acts as a saw or file and, given time enough, can cut through the hardest rocks. Ogden River was flowing west along its present course before the Wasatch Mountains came into existence. The raising of the mountains went on slowly for ages, so slowly that the river kept its place by cutting down its ever rising bed, carving a deep and narrow canyon straight through the block of the earth's crust as it rose. In no other way can we account for a river rising on one side of the range and flowing directly across it. Movement of the mountain mass has continued down to the present time—at least there has been recent disturbance along the base of the Wasatch Range, as is shown by faults which traverse the lake deposits and the modern alluvial aprons. Some of the breaks are so new as to be devoid of vegetation. Furthermore, the main stream channels crossing from the uplifted fault block to the undisturbed rocks on the west have abnormal profiles. Ogden River has a high gradient within the canyon, but on crossing the fault and emerging on the gravel fan at its mouth at once loses grade. The upward movement of the mountains has been so continuous that the river has had no opportunity to widen its valley, a task which it will begin as soon as the mountains cease rising.

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About a quarter of a mile east of The Hermitage, in the south wall of the canyon, a few feet above the river, the limestone is folded. The position of the thin strata, once nearly horizontal throughout but now turned abruptly back on themselves, suggests something of the stresses that have had a part in forming these mountains. A mile farther along in the road cut, near a flume that crosses the river, there is a very distinct S fold in black shales that indicates even more vividly the complexity of the mountain-making process. Some of this black shale contains phosphate.²

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²In a roadside ledge about 2 miles below the upper end of Ogden Canyon there is some black shale and limestone, which proves on analysis to be decidedly phosphatic. The richest material is contained in two beds of black shaly rock, each about 2 feet thick. Analysis of a random sample gives 42.5 per cent of bone phosphate. This deposit is too low in grade and too broken to be of value.

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The most prominent rock folding in the canyon is at the reservoir about 2-1/2 miles above The Hermitage. Here a thick bed of limestone is crumpled into a Z fold, measuring 1,000 feet between the top and bottom bars, which are about half a mile long. It can be seen plainly from the south bank of the reservoir. (See Pl. XXVI, A, p. 100.) This great wrinkle was made by the shoving of one mass of rocks over another during the formation of the mountain range.

At the upper end of Ogden Canyon, 10 miles from the city, is Ogden Hole or Ogden Valley, which, when Lake Bonneville reached its highest stage, was a small bay connected with the lake by a strait in Ogden Canyon.