and in part forested region, with mild, picturesque scenery. Perhaps a city park or the beautiful rural estates of England are most usually brought to mind when the term referred to is mentioned. But in the great mountains of the central portion of the continent one's idea must expand to keep in harmony with his surroundings. The natural parks of that region are broad, generally treeless, valleys with winding streams, the uplands are grass-covered and rolling, and in distant views the courses of the streams are marked by narrow belts of verdure. The picture is framed by a succession of mountain domes and embattled cliffs. Over all arches the dark blue, cloudless sky of a nearly rainless region. In the clear air distances are deceptive, and what appear to be miles to the novice must be extended to leagues in order to acquire adequate conceptions of the magnitude of the scene.
The most famous of the great tracts of generally level land surrounded by the high ranges of the Park Mountains is San Luis Park, situated in southeastern Colorado and extending southward into New Mexico, which has a length from north to south of about 130 miles, and is from 20 to nearly 40 miles wide. Its general elevation is between 7,000 and 8,000 feet. This great valley, level-floored with soft deposits swept in from the bordering highlands, and almost completely surrounded by rugged mountains, although more desolate than the majority of the numerous similar valleys in the same region, is typical of its class. The Rio Grande winds through its entire length and many streams rising in the bordering mountains flow to the valley during the winter season, but in summer, owing to the high temperature, active evaporation, and small rainfall, only a few of the larger of these mountain-born torrents reach the main, southward-flowing river. In the southern portions of the valley large areas are covered with drifting sand, which is fashioned by the winds into ever-changing dunes of a creamy whiteness. Some of the streams from the mountains expand on the plain and form the San Luis lakes, from which the water escapes by evaporation, thus causing them to become alkaline. The land bordering the lakes is whitened
as with snow by saline incrustations. On the lower portion of the rim of this mountain-inclosed basin there are scattered groves of pines and junipers, and at higher elevations the mountains are dark with forests. The more lofty peaks, however, rise far above the upper limit of the forests and are rugged and magnificent even under the glare of a cloudless sky.
To the east of the San Luis Park, and rising about 7,000 feet over it, and over 14,000 feet above the sea, stands Sierra Blanca, one of the finest of the many majestic mountains of Colorado. In summer immense cloud banks frequently gather about this cold, isolated peak, and local storms, accompanied by fierce lightning and echoing thunder, beat upon its shrouded sides. These tempests raging on the mountain top, while the adjacent valleys are flooded with sunlight, recall the scriptural accounts of the storms of Mount Sinai. In fact, the southwestern portion of the United States and the adjacent region in Mexico, so far as scenery and climatic peculiarities are concerned, have much in common with Palestine.
The other great parks in Colorado, which have suggested a name for the group of mountains in the midst of which they are sheltered, are less arid and less desert-like than the one just described; but like it, derive their magnificence and fascination from their vast extent, the sublimity of the bordering mountains, and the wonderful transparency of the air above them, rather than from the topography of their nearly level floors or the vegetation that strives ineffectually to clothe their nakedness.
The individual summits as well as the separate ranges composing the Park Mountains are remarkable for their massiveness and the great height of their bare rounded summits rather than for picturesque details. Several of the peaks are among the highest in the United States. One conspicuous feature is the considerable elevation of the valleys, usually over 7,000 feet, and the large number of lofty summits. Of the peaks that have been measured, over 30 exceed 14,000 feet in height. The portion of the Park Mountains above an elevation of 10,000 feet, as is indicated
on the map reproduced on page 65, is far greater in area than any other region of similar altitude on the continent.
In the Park Mountains, and generally throughout the southern Rockies, even to central Mexico, the forms that meet the eye are the remnants of vast upheaved folds and domes of the earth's crust sculptured and degraded by erosion. The nearly horizontal rocks of the Great plateaus on meeting the eastern border of the mountains are bent abruptly upward, and in many places stand on edge or have been overturned so as to dip westward. This abrupt upward bending and the presence of remnants of the same beds on the summits of some of the higher mountains shows that the strata have not been simply folded into anticlinals and synclinals, but that there has been a thickening and upswelling of the rocks beneath.
In the northern Rockies, except in western Idaho and adjacent portions of Washington and Oregon, evidences of recent volcanic activity are rare, although igneous rocks cover great areas, and in the Yellowstone Park numerous geysers and hot springs bear evidence to the presence of abnormal heat in the earth's crust. In the southern Rockies, however, volcanic mountains which still preserve their forms are numerous in certain regions, and in Mexico there are mighty volcanic piles and many lesser elevations built up by extrusion of molten material, some of which are still active. Examples are furnished of volcanic mountains ranging from perfect cones with curved slopes typical of the forms produced by the piling up of various sized fragments about the vents from which they were extruded, to irregular serrate peaks which reveal the anatomy of the dissected volcanic masses, and even the dikes which remain after the surface elevation of a volcano has been removed. The most modern volcanoes in this great group of mountains are situated in central Mexico, but others nearly as perfect in form occur in New Mexico and Arizona, and in the plateaus to the east of the Park Mountains. The Spanish peaks in southeastern Colorado are instructive illustrations of the topographic forms produced when a volcanic mountain has been deeply dissected.