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Show BEAR VALLEY. 193 Plateau and Lower Sevier Valley. As these last-mentioned formations have been inferred provisionally to be of Green River age, the beds of volcanic sand, &c, may form an upward continuation of the same group, or may even be considerably more recent, though many circumstances seem to indicate that they were deposited in immediate succession to the definite Green River beds without any protracted interval to separate them. Their significance is purely local. They indicate that the eruptive activity had commenced and had given vent to large masses of lava before the extravasation of the older volcanic masses now remaining, and that these most ancient ejections had been wasted and either utterly swept away or buried where they have not up to the present time been laid bare. These beds are seen in considerable mass on both sides of Upper Bear Valley, and on the southeast side they constitute the lower courses of the two mountains which tower above it and the long curtain wall which connects them. Resting upon them is a sheet of lava of very interesting character. It is identical in constitution with a sheet exposed in East Fork Canon, and which will be described in detail in the chapter on the Sevier Plateau. Upon this lava rests a layer of coarse rhyolite, which is evidently much more recent in age, and forms the summit wall of the west side of Upper Bear Valley. This layer is not seen on the eastern side, but in place of it numerous trachytic beds are found alternating with conglomerate. At the bases of the two mountains these same beds of volcanic sand are seen and the succession of trachytes and conglomerates. The upper masses of the. mountains are mostly trachytic, though between the flows there is one prominent conglomeritic mass. The stratification is remarkably even throughout, considering the volcanic nature of the components, but it is not horizontal. In both mountains there is an east or east-southeast dip, and they present the general aspect of great buttes left by the denudation of the surrounding country, though the similitude is not exact. A portion of their eminence, however, is due to a fault of about 800 feet displacement which runs along their western bases, and the remainder of their relative altitude is probably due to the denudation of the general platform to the east of them and to the dip of the beds. These eruptions are all very ancient (Miocene?), and since their extravasation they have 13 n p |