YELLOWSTONE NATIONAL PARK, an area situated mainly in north-western Wyoming, United States, which has been withdrawn from settlement by the United States Government and dedicated to the purposes of a public park. It is a region of hot springs and geysers, mountains and canons, lakes and waterfalls. While it is almost entirely comprised in Wyoming, a narrow strip 2 miles wide projects on the north into Montana, and on the west a strip about 5 miles in width projects into the same Territory and into Idaho. Its boundaries, which were defined at a time when the country was little known, are as follows. The northern boundary is a parallel of latitude running through the mouth of Gardiner river, a branch of the Yellowstone, 2 miles north of 45° N. The eastern boundary is a meridian 10 miles east of the most easterly point of Yellowstone Lake, which places it almost on the 110th meridian. The southern boundary is a parallel 10 miles south of the most southerly portion of the same body of water, in lat. 44° 10'N. The western boundary is a meridian 15 miles west of the most westerly portion of Madison (now Shoshone) Lake, this meridian being approxi-mately that of 111° 6'. The Park is therefore very nearly a rectangle in shape, its length north and south being 61'8 miles and its breadth 53"6. Its area is 3312 square miles.
Its surface is mainly an undulating plateau, with a mean elevation above tlie sea of about 8000 feet, upon the surface of which the minor streams flow, while the larger ones have cut canons for themselves, several of them being of great depth. The eastern portion, however, is occupied by an extremely rugged mountain chain, known as the Absaroka Range, peaks of which rise to heights exceeding 11,000 feet. These mountains, which separate the waters of the Yellow-stone from those of the Big Horn, are unsurpassed in the United States for sublimity and grandeur of scenery. The Gallatin Range, which separates the Yellowstone from the Gallatin river, enters the Park near the north-western corner and extends southwards some 20 miles within it. It reaches its culminating point in Electric Peak, 11,050 feet high, just within the Park boundary. Another group of mountains, in the form of a horseshoe, occurs near the middle of the Park, known as the Washburne Mountains, the highest summit of which, Mount Washburne, has an elevation of 10,346 feet. The Red Mountains are in the southern part, their culminating peak being Mount Sheri-dan, 10,385 feet in height. In this part of the Park the plateau is more elevated and broken, and just beyond its southern limits it rises into a confused maze of mountains.

The Park has an abundant rainfall, and its streams are numerous and bold. It contains many beautiful lakes and ponds. Within its area are the sources of the Yellowstone and the Madison, which go to make up the Missouri, and of the Snake, one of the forks of the Columbia. This last stream, which drains the south-western part, takes its rise in several branches, among them being Lewis Fork, which has its origin in the beautiful Shoshone Lake, and Heart river, which rises in Heart Lake, under the shadow of Mount Sheridan. The Yellowstone drains the eastern part. Rising just beyond its southern limits, it flows into and through Yellowstone Lake, a magnificent sheet of water, of very irregular shape, having an area of 150 square miles. A few miles below the lake, the river, after a succession of rapids, leaps over a cliff, making the Upper Fall, 112 feet in height. Half a mile lower down it rolls over the Lower Fall, which has a clear descent of 300 feet. The river at this point carries, at the average stage of water, about 1200 cubic feet per second. With this fall the river enters the Grand Canon, which in many scenic effects has not its equal on the globe. Its depth is not great, at least as compared with the canons upon the Colorado river system, ranging from 600 feet at its head to 1200 near the middle, where it passes the Washburne Mountains. Its length to the mouth of Lamar river is 24 miles. It is cut in a volcanic plateau, and its ragged broken walls, which are inclined at very steep angles, are of a barbaric richness of colouring that almost defies description. Reds, yellows, and purples predominate, and are set off very effectively against the dark green of the forests upon the plateau, and the white foam of the rushing river which fills the bottom of the chasm. Near the foot of the Grand Canon, Tower creek, which drains the concavity of the horseshoe formed by the Washburne Mountains, enters the Yellowstone. Just above its mouth this stream makes a beautiful fall of 132 feet into the gorge in which it joins the river. A few miles farther down the Yellowstone is joined by an eastern branch, Lamar river, which drains a large part of the Absaroka Range. Then it enters the Third Canon, from which it emerges at the mouth of Gardiner river. The latter stream drains an area of elevated land by means of its three forks, and upon each of them occurs a fine fall in its descent toward the Yellowstone. The Madison rises in the western part of the Park and flows in a generally north-ward and then westward course out of the Park. Its waters are mainly collected from the rainfall upon the plateaus, and from the hot springs and geysers, most of which are within its drainage area. Upon this river and its affluents are several fine falls. Indeed all the streams of this region show evidence, in the character of their courses, of a recent change of level in the surface of the country.

The climate is characterized by a considerable degree of humidity and a heavy rainfall, as compared with adjacent portions of the West. The temperature is that of a semi-arctic region. Frost may occur in midsummer and snow begins to fall in September.

The native fauna is abundant and varied. The policy of the Government, which protects game within this reservation, has in-duced it to take shelter here against the sportsman and pot-hunter, so that elk, deer, antelope, mountain sheep, bear, and numerous smaller game animals are very abundant and tame. The only herd of wild bisons left in the United States is upon this reservation ; and in some parts moose are occasionally seen.

The flora is very varied. With the exception of a few limited areas in the northern part, the region is covered with forests, gener ally so dense that landmarks are invisible and the traveller is forced to guide himself by the sun or by compass. The trees are mainly the Douglas spruce and the yellow pine, and are not of large size or great commercial value.

The surface of the park is almost entirely covered with volcanic rocks. The Gallatin Range, however, in the north-western corner, is made up of stratified beds ranging from the Silurian system up to the Cretaceous. In a few localities also Tertiary lake beds and local drift are found. The plateaus generally are composed of rhyolite, while the mountain ranges are made up of later volcanic deposits, mainly conglomerates. In this region the ancient volcanic fires, which formerly extended far and wide, especially to the south and west, are still in existence, as is shown by the vast numbers of hot springs and geysers. The number of the former is by a closs estimate not less than S000, varying in size from a few inches in diameter to an area of many acres. The number of active geysers is 71. These phenomena are found in groups in numerous local-ities, the most important of which—for they contain most of the great geysers—are the Upper and the Lower Geyser basins near the head of the Madison, here known as the Firehole, river. The former contains 26 geysers, several of which are of such power as tc throw water to heights exceeding 200 feet, and the amount or water thrown out is so great as to raise the temperature of the river water many degrees. The Lower basin contains 16 geysers. The Norris basin, upon Gibbon river, a branch of the Madison, contains 9 geysers, and the Shoshone basin, upjon the shore of Shoshone Lake, contains 8 active spouters. Others are found at Heart Lake, upon Pelican creek, in Hayden's valley, and in Monument basin. In all these localities the water holds silica in solution in considerable quantities, so that as it cools and evaporates it deposits siliceous matter, which has covered with a hard wdiite floor many square miles of these valleys, and has built up craters around the springs and geysers of considerable size and great beauty of form. Besides silica, the water of many of the springs contains sulphur, iron, alum, and other materials in solution, which in places stain the pure white of the siliceous deposits with bright bands of colour. Upon Gardi-ner river, near the northern boundary of the Park, there is a large group of springs, known as the Mammoth Hot Springs, which differ from the others in holding cai Donate of lime in solution. These springs have deposited so freely as to build up a hill 200 feet in height, from the top of which the springs boil out. The slopies of this mound have been built in the form of a succession of basins rising one above another, and the water from the springs overflows from one into another, growing gradually cooler as it descends. Upon the bank of Yellowstone river, between the falls and the lake, there was, when the region was first explored, a geyser which at intervals of about 4 hours threw up a column of mud to a height of 40 or 50 feet. In more recent times this geyser has ceased action. These phenomena have been under observation since 1871 ; and, while there have been changes in them, certain geysers having ceased and others having been formed, no evidence of a diminution of power has been observed.

The Park is accessible by means of the Northern Pacific Railroad, by a branch which extends up the valley of the Yellowstone within a few miles of the northern boundary and with this a line of stage coaches is connected.

The most stringent laws have been enacted in regard to the killing of game, the starting of forest fires, and the removal of the deposits of the springs.

Although exploring parties had at various times passed on all sides of this strange region, its wonders remained undiscovered until so late a period as 1870. This fact is all the more remarkable because at that time the frontier of settlement was in the Gallatin valley, not a hundred miles from the great geyser region. Some rumours of hot springs and geysers, coming from stray trappers and Indians, had been received, however, and these were sufficient to start a party from the Montana settlements in 1870, to investigate the strange tales. The discoveries made by this, the Washburne party, induced Dr F. V. Hayden, then in charge of a Government survey. to turn his explorations in this direction. The reports brought back by him induced Congress to reserve this area from settlement, which was done in the spring of 1872. In that year further explorations were made, and in subsequent years army expeditions carried the work of exploration still farther. In 1878 a map of the Park, based upon triangulation, was drawn up by the Hayden survey, and in 1883-85 a more detailed map was made by the United States Geological Survey, and a systematic study of its geological phenomena was instituted. (H. G*.)