Encyclopædia Britannica, Ninth Edition/Wyoming

WYOMING, a Territory of the United States, is nearly rectangular in shape, having as its boundaries the 41st and 45th parallels of N. latitude and the 27th and 34th meridians west of Washington. South of it are Colorado and Utah; on the west, Utah, Idaho, and Montana; on the north, Montana; and on the east, Dakota and Nebraska. The area is 97,890 square miles.

The surface is greatly diversified. Its mean elevation is great, being probably not less than 6400 feet. The lowest portions of the Territory are along the northern and eastern borders, where in several places the surface is less than 5000 feet above sea-level, while its highest points exceed 13,000 feet. By far the greater part consists of high plains, which are broken by numerous mountain ranges and ridges, which form parts of the Rocky Mountain system. This system enters the Territory in the south-eastern part, and traverses it in a north-west direction. On the south it consists of three members, the Laramie range, which is crossed by the Union Pacific railroad at Sherman, and the Medicine Bow and Park ranges, which separate branches of the North Platte river. These ranges run out and fall down into the plain in the southern part of the Territory, leaving for 150 miles a broad flat plateau to represent the Rocky Mountain system. The ill-defined summit of this plateau forms the parting between the waters of the Missouri and Colorado. Eastward this plateau slopes to the Great Plains, and westward to the Green river basin, The Union Pacific Railroad traverses it, and therefore the traveller upon this road sees little of the Rocky Mountains except at a distance. Farther north the mountains rise again from this plateau in several ranges. The principal of these is that known as the Wind River range, which in a sense is continued northward beyond the northern boundary of the Territory by the Absaroka range. The former contains the most elevated land in the Territory, its highest peak being Frémont's, with an elevation of 13,790 feet. The latter range is in its southern part a great volcanic plateau, elevated 10,000 to 11,000 feet above the sea, while farther north it is eroded into very rugged mountain forms. About the point where these ranges join, there is a confused mass of mountains of great breadth and considerable height. In this elevated mass rise streams flowing to the Atlantic, the Gulf of California, and the Pacific. The highest peaks of these mountains are those known as the Three Tetons, the most elevated of which, Mount Hayden, has an altitude of 13,691 feet. East of the Wind River and Absaroka ranges, and separated from them by the valley of the Wind River and the Big Horn basin, is the range

known as the Big Horn Mountains, which is reputed to contain peaks having an altitude of 12,000 feet. These ranges form the backbone of the Territory. Eastward from the Big Horn and Laramie ranges stretch the plains in an almost unbroken expanse, gently sloping to the eastward from an altitude of about 6000 feet at the base of the mountains, while south-west of the Wind River range is spread the expanse of the Green river basin, through which flows the principal fork of the Colorado.

The drainage system of Wyoming is somewhat complex. While the mountainous regions are well watered by numerous streams, the broad valleys and the plains are poorly supplied with streams. Many of those which flow full in the mountains during the entire year run dry in summer upon the plains. None of the streams are navigable. The eastern three-fourths of the Territory is drained by the tributaries of the Missouri to the Atlantic. Of this area the North Platte drains the southern portion of the Rocky Mountain system, together with a large part of the plains lying north and east of it. Farther northward and eastward the plains are drained by the Cheyenne river. The eastern face of the Big Horn mountains is drained by the Powder and Tongue rivers, while from its western slopes, and from the eastern slopes of the Wind River and Absaroka ranges, the Wind River, known lower down in its course as the Big Horn, collects the waters. The Yellowstone, heading in the confused mass of mountains about the north end of the Wind River range, flows northward through a beautiful lake, draining the west slope of the Absaroka range. The Snake, or &ldquo;Mad&rdquo; river of the early explorers, heading in the same mass of mountains, flows south-westward to seek an exit from them, while the Green, whose sources are in the same elevated country, drains the west slope of the Wind River range, and flows southward through the broad sage-covered expanse known as the Green river basin. In the south-west corner of the Territory is a small area drained by means of Bear river into Great Salt Lake.

The geological structure of Wyoming is even more complicated than its surface features. In the north-western corner is an area in which volcanic action, as represented in hot springs and geysers, is still alive, while the evidences of volcanic action upon a tremendous scale, in recent geological time, are seen in the form of sheets of lava and volcanic breccia, which are spread over the land, and from which mountain ranges have been carved. Most of this region is comprised in the (q.v.), which has been set apart from settlement by the general Government. Many of the mountain slopes show a succession of the stratified formations, from the Triassic downwards through the series. The plains region is mainly floored by Tertiary and Cretaceous formations, as is also the case with the higher plateaus and with the Green river basin.