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

SHEET No. 3. (click on image for an enlargement in a new window)

Near Central City (see sheet 3, p. 26), the traveler passes from the Niobrara limestone, of Cretaceous age, to the formations of Tertiary age.¹ (See table on p. 15.) If the younger Cretaceous formations, the Pierre shale, Fox Hills sandstone, and Laramie formation, were ever deposited here, they were eroded away before the Tertiary beds were laid down. The contact therefore denotes a very long period of time during which the older sedimentary formations were being eroded.

---

¹In marked contrast with the Cretaceous formations, which were laid down in shallow marine water and which are regular in thickness and character over vast areas, the Tertiary deposits of this region are irregular in thickness and character, are nonmarine, and were deposited along streams or in shallow lakes. During the Cretaceous period Nebraska and certain other parts of central North America lay beneath the sea, but with the Tertiary period began a new order of things. The sea, which had extended from Iowa to Utah, was expelled by uplift from the interior of North America, and in the midst of the region the sea formerly covered the Rocky Mountains began to rise. It is this change from a quiescent sea to mountainous uplands, with all the disturbances attending it, that marks the division in geologic time between the Cretaceous and the Tertiary period. If at the present time the waters were expelled from the Gulf of Mexico and high mountains raised in their place, the resulting changes in climate, geography, etc., would be less conspicuous than those which marked the change from Cretaceous to Tertiary in the interior of North America.

The earth movements that formed the Rocky Mountains also brought the Great Plains and the intermontane basins above sea level, so that the region now traversed by the Union Pacific from Omaha to the Wasatch Mountains, which had formerly lain under the water of the sea, was changed to dry land and, so far as is known, has never since been covered with sea water. The plains were doubtless very low—not much above sea level at first. Rivers heading in the newly upheaved mountains washed sediment out upon low-lying plains, where it accumulated because the streams were too sluggish to carry it away. This newly emerged land became inhabited by animals, some of which were doubtless developed from ancestors that lived in North America during Cretaceous time, though others immigrated from other continents. The skeletons of these animals were buried in the sands and muds deposited by the streams, and from the fossil remains of their bones the paleontologist is able to determine to some extent their forms, appearance, and habits.

Great changes took place also in the climate, a fact indicated by the character of the plants, a critical study of which shows that although the same general types of vegetation that had flourished throughout the Cretaceous continued into the Tertiary the species were nearly all different.

---

Grand Island, the seat of Hall County, is a railroad center, a division station of the Union Pacific, where extensive shops are maintained, and a city of considerable commercial importance, having numerous factories and mills. It is in an agricultural district where the raising of sugar beets is one of the principal industries. About 7,000,000 pounds of granulated sugar is produced here every year. The first known reference to Grand Island is contained in the account of Robert Stuart, an employee of John Jacob Astor, who left Astoria in 1812 and traveled eastward over what was later known as the Oregon Trail. The greater part of this journey was made through a country then wholly unknown. "Le Grande Isle" was the first place he was able to recognize on his way east. Grand Island, a strip of land about 42 miles long, included between two channels of the Platte River, had previously been visited by trappers, most of whom were French Canadians, but white people did not settle here until 1857. In 1866 the Union Pacific was built north of the north channel and the site of the city of Grand Island thus determined.

Grand Island is in the midst of what was formerly known as the great buffalo range. Gen. Dodge says:

When the railroad reached this point, in 1866, buffalo were numerous. In the spring these animals were wont to cross the Platte from the Arkansas and Republican valleys, where they had wintered, to the northern country, returning again, sleek and fat, late in the fall. Gradually their numbers decreased on this range until 1873, when they disappeared. But at Julesburg, 219 miles farther west, a small band was seen to cross the river as late as 1876. In 1860 immense bands were on these plains. On the south side of the Platte, on the old emigrant road, the number was so large that emigrant teams often had to stop while they were crossing the road. At Fort Kearney, on the south side of the river, in 1860, an order was issued by the post commander, forbidding the soldiers to shoot the buffalo on the parade ground.

Some attempts have been made in the region of Grand Island to sink wells to the Dakota sandstone to obtain artesian water. A well put down for the city some years ago penetrated 220 feet of sand, gravel, and clay, consisting of river deposits and probably also of some Tertiary material, and then went through shale to a depth of 935 feet without finding the sandstone. The artesian stratum therefore lies at some greater depth. At Hastings, about 25 miles farther south, a well 1,145 feet deep entered sandstone that may be the Dakota.

On leaving Grand Island the train passes through the middle of the valley, which is here 22 miles wide. From anything the traveler can see from the train he might imagine himself to be passing over a boundless plain, for the bluffs on either side of the valley are too far away to be distinguished. The surface looks level, but as a matter of fact it rises toward the west about 10 feet to the mile. No surface depression, such as the term "valley" might lead one to expect, can be seen. The river flows in many interlacing channels that frequently shift their position.

Over this part of the route there are long stretches of straight track. West of Silver Creek the train runs for 40 miles in a nearly straight line. The roadbed is remarkably smooth and free from dust, being ballasted with Sherman granite. (For description see p. 43.) This part of the route is on the typical Great Plains,¹ which rise gradually but regularly from the prairies of Mississippi Valley to the Rocky Mountains.

---

¹The Great Plains constitute that part of the continental slope which extends from the Rocky Mountains eastward to the prairies of the Mississippi Valley. Smooth surfaces characterize most of this area, but in some parts of it there are buttes or flat-topped hills and long bluffs or escarpments. In other places there are large areas of bad lands and sand hills.

The origin and development of the Great Plains are difficult to determine. From Omaha westward to the Laramie Range, a distance of more than 500 miles, the surface rises with a regular inclination that is imperceptible to the eye but amounts to more than 5,000 feet. The rocks of this area, aside from the thin Tertiary formations and the superficial deposits, are of marine origin; they were formed below sea level. Later they were tilted, but without notable warping, through this great distance and beveled by erosion, so that the surface of the plains region extended across the eroded edges of the Cretaceous formations from oldest to youngest. On this surface were later spread out the stream deposits of Tertiary and Quaternary age, and at the extreme east the glacial deposits.

A good illustration of this grading process is furnished by Platte River, which flows in a shallow valley cut slightly below the surface of the plains and has the same gradient or slope as the plains themselves. This gradient is in nice adjustment to the load of sediment that the river carries, so that although during past ages the Platte sometimes cut its channel deeper than it is at present and sometimes built it up, as it seems to be doing now, it has on the whole spent its energy in widening its valley and forming remarkably even bottom lands. If this process goes on long enough the Platte and its neighboring streams will form new Great Plains, slightly lower than the present plains but having essentially the same eastward inclination. On the other hand, should some condition arise whereby the sediment supplied to these rivers would be increased in volume not only might the present valleys be filled with sand, gravel, and clay, but the whole surface of the plains might be built up, the conditions thus supposed to exist simulating the conditions that prevailed in this region during middle and late Tertiary time.

---

West of Wood River are Shelton and Gibbon, agricultural and stock-feeding centers. Two small towns, Optic and Buda, are next passed by the train before it enters Kearney.