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Show 174 GEOLOGY OF THE HIGH PLATEAUS. of craters, but mere remnants of the uppermost sheets, which have been almost wholly removed by erosion. From their bases radiate profound gorges separated by huge buttresses, which extend to the lowest valleys and plains, while beyond them rough crags and shattered domes rear their bald summits to the clouds. But all this grand detail of mountain form has been carved out of the vast block of the tabular mass by the ordinary process of erosion. The lavas accumulated sheet upon sheet, the subterranean forces uplifted the block and tilted it, and the rains and torrents have done the rest. The eastern front of the Tushar is far more rugged and mountainous than the western, and the explanation is obvious. The western slope is along the dip of the strata, which, though considerable near the crest, is slight as we recede from it westward. The eastern slope is across the upturned edges, and from the nature of the case is very abrupt. The power of water to corrade and carve rapidly increases with the slope, and the resultant sculptural forms are correspondingly bold and craggy. The loftiest, boldest, and most diversified portion of the Tushar fronts the Sevier Valley in the vicinity of a little hamlet called Marysvale, situated about 27 miles south of Richfield. The great mountain wall leaps at once from the narrow platform of the valley to nearly its greatest altitude. Immense ravines, rivaling those of the Wasatch in depth, but narrower and with steeper sides, have deeply cleft the great tabular mass, and subdivided it into huge pediments, which from below appear like individual mountains. The finest gorge is named Bullion Canon, in the jaws of which the little village of Marysvale is situated. Ascending it, wre may gain some information concerning the structure of this portion of the Tushar mass. The lowest beds forming the base courses of the uplift are quartzites resulting from the metamorphism of sedimentary strata, which are believed to be of Jurassic age. They are considerably disturbed, yet not excessively so. The prevailing dip is to the west, though it is by no means uniform. The main fault, which has thrown down the platform of the Sevier Valley, runs north and south along the base of the mountains, but the whole displacement is probably by a series of parallel repetitive faults. I have seen but one of the faults west of the principal displacement, but have inferred |
