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

On leaving Council Bluffs the train gradually rises on a filled incline, about 2 miles long, to the bridge, which is about 60 feet above the ordinary water level of Missouri River. From this incline a good view may be obtained of the broad flood plain over which the river winds in a constantly changing course and upon which at times of flood it deposits the rich loam gathered from the vast areas it drains. The productive fields that present so pleasing an aspect during the growing season and give the appearance of opulence at harvest time are the direct result of this constant activity of the river. But neither these fields nor anything else on the bottom lands can be regarded as permanent, for the great river is continually eating away the plain in some places and building it up in others. This action causes the stream to assume a winding course—that is, to meander in loops and bends that are called oxbows. In this process of shifting its course, when these bends become very sharp the river tends to straighten itself by cutting across the narrow necks, and it thus abandons parts of its former channel, which become bayous, or oxbow lakes. Cutoff Lake, which can be seen to the right,¹ 3 miles north of the bridge, is one of these abandoned oxbows. At the time the river was agreed upon as the boundary between Iowa and Nebraska. Cutoff Lake was a part of its channel, but in 1870 it straightened its course, so that the land partly inclosed by Cutoff Lake, although a part of Iowa, now lies west of the river and is almost surrounded by territory belonging to the State of Nebraska. This shifting of the river's course can be prevented to some extent by building levees, or embankments. North of Council Bluffs an embankment has been thrown up and faced with a hard quartz rock (Sioux quartzite) which was shipped for this purpose from Sioux Falls, S. Dak., 160 miles away. The necessity for this protection is obvious, for some of the lowland near Council Bluffs lies below river level.

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¹The terms right and left as employed throughout this book apply to the westbound journey.

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The building of the bridge² was regarded as a notable feat of engineering, and its present importance is indicated by the fact that the traffic of seven railroads passes over it. It spans one of the longest rivers in the world, the Missouri and Mississippi combined, 3,820 miles long. The bridge crosses this great river 669 miles above the junction with the Mississippi, and the drainage from 323,000 square miles, including large parts of Montana, North Dakota, and South Dakota, passes under it. The water surface has a known range of level of 25 feet at this point; the lowest water recorded was in 1867, and the highest in 1881. The discharge at Omaha averages about 50,000 second-feet; that is to say, on the average, 50,000 cubic feet (374,000 gallons) of water passes under the bridge every second.

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²The first bridge built at Council Bluffs was begun by the railroad company in 1869 and completed in 1872 at a cost of $1,750,000. It carried a single track, consisted of 11 spans, each 250 feet long, and was about 60 feet above ordinary flood level, or 50 feet above the highest recorded level. This height served two useful purposes—it brought the track to the level of the bluffs west of the river and allowed boats which were formerly used on the river to pass under it, thus obviating the necessity of a drawbridge. The two eastern spans of this bridge were wrecked by a tornado in 1877, but the bridge was used with temporary repairs until 1886, when it was replaced by the present double-track structure.

The river here during low water is about 900 feet wide. The bridge over the main channel rests on five piers, 250 feet apart, that extend to bedrock at a maximum depth of 76 feet below the level of the flood plain. These were built midway between those of the old bridge. (See diagram on sheet 1, p. 18.) They carry the four main spans, and on each end are three additional deck spans, making the total length of the bridge 1,750 feet. Although the records give no intimation of the kind of rock on which the piers rest, it is supposed to consist of limestone and sandstone of Carboniferous (Pennsylvanian) age, which are known from well borings to underlie the glacial drift in the vicinity of Omaha. These rocks are exposed in the river bluffs near South Omaha but can not be seen from the train.

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Although designed to accommodate foot passengers and wagons, the bridge has never been so used. Local traffic passes over the bridge of the Omaha & Council Bluffs Street Railway Co., half a mile farther north, and beyond this is a drawbridge of the Omaha Bridge & Terminal Co., over which pass the trains of the Illinois Central Railroad.

The Missouri is the muddiest river in the Mississippi Valley; it carries more silt than any other large river in the United States except possibly the Rio Grande and the Colorado. For every square mile of country drained it carries downstream 381 tons of dissolved and suspended matter each year. In other words, the river gathers annually from the country that it drains more than 123,000,000 tons of silt and soluble matter, some of which it distributes over the flood plains below to form productive agricultural lands but most of which finds its way at last to the Gulf of Mexico.

It is by means of data of this kind that geologists compute the rate at which the lands are being eroded away. It has been shown that Missouri River is lowering the surface of the land drained by it at the rate of 1 foot in 6,036 years. The surface of the United States as a whole is now being worn down at the rate of 1 foot in 9,120 years. It has been estimated that if this erosive action of the streams of the United States could have been concentrated on the Isthmus of Panama it would have dug in 73 days the canal which has just been completed, after 10 years' work, with the most powerful appliances yet devised by man.

Nebraska lies mainly in the Great Plains province of the western United States, in altitudes ranging from 842 to 4,849 feet above sea level, and is drained to the Missouri through the Niobrara, the Platte, and many minor streams. The annual rainfall in the State ranges from 13.30 to 31.65 inches and averages 23.84 inches. Dry farming is general and large crops of corn, wheat, and oats are raised. Nebraska claims a greater variety of native grasses than any other State in the Union, their number amounting to more than 200, of which 150 are valuable for forage. In the western part of the State some irrigation is practiced.

Nebraska is primarily an agricultural State and has been called "a State without a mine," but it does contribute to the country's mineral production by some utilization of its clay resources, by a considerable output of sand, gravel, and building stone, and by a practical monopoly of the country's production of volcanic ash, or pumice. The packing industry is large.

The State includes 77,520 square miles and in 1910 had a population of 1,192,214.

The name Omaha is derived from that of a tribe of Indians that once inhabited this region. The first white settlement was made in 1854, but not until railroad construction began, about 10 years later, did it become a town of importance. Here ground was broken December 1, 1863, for the construction of the road, although little real construction work was done before the spring of 1865; here the first transcontinental train started for San Francisco on September 13, 1870; here occurred on November 1, 1897, "the world's greatest auction," when the Union Pacific, which had cost $115,214,587.79 to construct, was sold for $57,564,932.76; and here are situated the offices, shops, and general terminal facilities of the Union Pacific system.

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¹The figures given for population throughout this book are those of the United States Census for 1910. For unincorporated places the census figures give the population of the election precinct, township, or other similar unit; such figures are marked with an asterisk (*).

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The station at Omaha is built in a depression eroded in loess (see p. 8), and good exposures of this peculiar material may be seen on the left as the train leaves the station. Thence westward to Elkhorn it lies on either side of the track, through the entire length of the Lane cut-off, which is one of the notable engineering features on the Union Pacific route. Prior to 1908 the trains passed through South Omaha and thence up Papillion Creek to Elkhorn. To avoid this circuitous route a line was built nearly due west from Omaha, cutting to a maximum depth of 85 feet straight through the numerous hills and building across the broad valleys, making, at a cost of $3,000,000, a level road bed nearly 12 miles long, which shortened the line by about 9 miles.²

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²The material visible in these cuts is mainly loess and clay. In some places the glacial till under the clay is exposed, but the two can not be distinguished from the train. In nearly all the cuts, however, the division between the loess and the clay is readily discernible. The upper part of the bank in each cut consists of buff-colored loess 30 to 50 feet thick and is rather sharply separated from the lower part, which consists of brick-red clay. A somewhat singular relation may be observed in these cuts. The red materia] is exposed only in the center of each cut, and its surface in cross section has practically the same outline as the surface at the top. (See fig. 2.) The overlying loess is of nearly the same thickness in all places, as if it were a uniform blanket spread over an older surface that had the same shape as the present surface.

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FIGURE 2.—Sketch profile showing relation of loess to underlying beds of clay and glacial till in railroad cuts west of Omaha, Nebr.

The city of Omaha is built on loess, and wherever grading has been done or excavations have been made the characteristic steep walls of this material may be seen. The loess is fine grained, massive, and compact and carries numerous small light-colored limy concretions. Nearly vertical walls of it have stood practically unchanged for 30 years, and other equally precipitous walls have the appearance of being much older.

The blanket of glacial debris and loess (see fig. 2) overlies limestone and sandstone of Carboniferous age,¹ which have been penetrated by a time when most of the coal beds in the eastern part of the United States were in numerous wells bored for artesian water, but which can not be seen from the train. The Carboniferous period was so named because in many parts of the World its rocks contain an abundance of carbon in the form of coal. In the central and eastern parts of the United States much coal is interlayered with rocks of this age, but only one coal bed has been found in the Carboniferous rocks of Nebraska, and that one is not of much economic value under present conditions. Attempts to mine it have not proved successful.

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¹The only Paleozoic rocks which come to the surface in eastern Nebraska belong to the Carboniferous system, deposited at process of formation from vegetal deposits. (For types of Carboniferous vegetation see Pl. IV, C, p. 20.) They are economically the most important rocks in the State. Most of the building stone, clay, and lime produced in Nebraska come from them. Their relations to other rock formations exposed in eastern Nebraska are shown in the following table:

Geologic column showing relations of rocks exposed in eastern Nebraska.

Age.	Formation.	Character.
Quaternary.	Loess.
	Kansan drift.	Glacial till.
	Aftonian gravels.	Sand and gravel; locally conglomerate.
	Pre-Kansan or Nebraskan drift.	Glacial till.
Tertiary.		Sand and clay.
Cretaceous.	Niobrara limestone.	Chalky limestone and shale.
	Benton shale.	Blue shale with limestone concretions (Carlile shale.)
		Hard slaty limestone and blue chalky clay. (Greenhorn limestone.)
		Dark sandy shale. (Graneros shale.)
	Dakota sandstone.	Soft massive yellow sandstone.
Carboniferous		Limestone, sandstone, and shale of Permian and Pennsylvanian age.

In eastern Nebraska the Carboniferous beds that appear at the surface comprise 200 feet of Permian and 1,200 feet of Pennsylvanian rocks. The lowest series of the Carboniferous, the Mississippian, does not outcrop here. The Pennsylvanian rocks consist of alternating limestones and shales. The rock formations below the Pennsylvanian in eastern Nebraska are of interest because they include certain strata that supply water to artesian wells. Several of these wells drilled in and near Omaha found water at depths of 1,200 to 1,800 feet under pressure sufficient to flow at the surface. The lowest stratum yields the strongest flow.

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