Page:EB1911 - Volume 28.djvu/939

Rh YELLOWSTONE NATIONAL PARK, an American national reservation, situated mainly in N.W. Wyoming, U.S.A., dedicated by the United States government as "a public park or pleasure ground for the benefit and enjoyment of the people." It is nearly a rectangle in shape, with a length, from N. to S., of 62 m., a width of 54 m. and an area of approximately 3350 sq. m. It extends into Montana, on the N., about 2¼ m. and into Montana and Idaho, on the W., 2 m. Except at its main entrance, through the valley of the Yellowstone on the N., the park is entirely surrounded by national forests: the Gallatin and Absaroka national forests, on the N.; the Shoshone and the Beartooth, on the E.; the Teton, on the S.; and the Targhee, the Madison and the Gallatin, on the W.

The central portion, comprising an area of about 2000 sq. m., is an undulating volcanic plateau with a mean elevation above the sea of about 8000 ft. Along the entire E. border stretches the Absaroka range, with peaks exceeding 11,000 ft. (Index Peak, 11,740 ft.) in height. On the N. is the Snowy range with its snow-capped peaks. W. of the Snowy the Gallatin range extends S. for 20 m. along the W. border. Electric Peak, in the N.W. corner of the park, rises to a height of 11,155 ft. Near the S. end of the park are the Red Mountains, which culminate in Mt. Sheridan (10,385 ft.) and afford a magnificent view of the whole region; and farther S. the N. spur of the lofty Tetons juts across the S. border.

In the production of these mountains and plateau there was first, at the close of the Cretaceous period, an upheaval of the earth's substance to form a mountain rim and a depressed basin. Subsequently, in the Tertiary period, there were two enormous outpourings of volcanic material—first andesitic lava, and later, after a long interval of quiet, rhyolitic—which nearly half filled the basin, converted it into a plateau and broke up the mountain rim. Two centres of volcanic activity were Mt. Sheridan, in the S., and Mt. Washburn, in the N. The volcanoes have long been extinct, but the diminished energy now causes hot springs and geysers in all parts of the plateau, about 100 in number. More than half, including the largest and finest, are in the upper and the lower Geyser basins, near the bead of the Madison, here known as the Firehole, river. Several others are farther N. in the Norris basin upon Gibbon river, a branch of the Madison, and others are farther S. in the Shoshone basin.

The Continental Divide crosses the park in a S.E. direction from the meeting-point of the states of Wyoming, Idaho and Montana. The small section S. of the Divide is drained by the Snake river into the Columbia river and the Pacific Ocean; the large section N. of the Divide is drained by the Yellowstone and Madison rivers into the Missouri, the Mississippi and the Gulf of Mexico. The Lewis river, a fork of the Snake, has its origin in the beautiful Shoshone Lake, and the Heart river, another fork of the Snake, rises in Heart Lake, under Mt. Sheridan.

The climate, influenced by the high elevation, is characterized by long and severe winters and short summers with great diurnal extremes of temperature. But the low temperature causes the moisture-laden winds to deposit here greater quantities of rain and snow than in the semi-arid regions below, which not only promote the growth of vegetation, but cause the activity of the springs, geysers and waterfalls. The mean annual temperature at the station of the United States Weather Bureau, near the N. boundary, is 39° F. The summer (June, July and August) mean is 59°; the winter (December, January and February) mean, 20°.

About four-fifths of the park is covered with dense forests of black pine (Pinus Murrayana), balsam, fir, spruce, cedar and poplar. These trees do not attain a large size. A low blueberry (Vaccinium myrtilis) forms a thick underbrush in much of the forest. Choke-cherries, gooseberries, buffalo berries, red currants and black currants grow along the streams and in moist places of the lower altitudes. In the glades are