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Show being introduced from below. The structure in these hills is easy to see and presents an impressive story when understood, especially in Slate Mountain, where a road affording spectacular views makes many of the features readily accessible. Sunset Crater, a recent cinder cone preserved as a national monument, already has received recognition as an outstanding natural feature, though only a beginning has been made in presenting its story so that the layman can see and understand it. Another cinder cone of unusual interest, and one that is little- known, is Red Mountain. Erosion has cut away the north side of this cone, clearly exposing to view the sloping layers of bright red cinders, thus demonstrating the manner in which it has been built up. Among features of special interest on San Francisco Mountain are evidences of glacial activity including moraines and outwash plains, areas of obsidian or volcanic glass, and plugs or necks showing where molten material came up through the interior at several different times. Features of the adjoining volcanic field that deserve mention because of their unusual character are the " squeeze- ups" and ice cave near Sunset Crater, the large lava tube known as Government Cave, and the Grand Falls of the Little Colorado formed by a lava dam. White Mountain volcanic field.- Along the southeastern margin of the Colorado Plateau in Arizona, east of longitude 110°, the plateau surface and much of the area to the south is thickly mantled with volcanic rocks of relatively late geologic age. The highest elevations are reached at such important centers of eruption as Ord Peak and Mount Baldy, around 11,000 feet. Southward from here, the volcanic field includes the Blue Range and extends to the vicinity of Clifton and Morenci. Eastward, it goes far into New Mexico, while in the west, many lava flows extend down into the Apache Indian Reservation, especially in the area east of Eagle Creek and north of the Gila River, on the Natanes Plateau south of the Salt River, and down Forestdale Creek farther north. The mantle of igneous rock forming this volcanic field varies greatly in thickness and in corn- Figure 27.- Sunset Crater in Arizona. 49 |
