OCR Text |
Show DOG VALLEY. 189 to the country at large rnay be comprised in the statement that it is an excellent illustration of what Powell has called the Kaibab structure. The length from north to south cannot be definitely given until we can fix its northern boundary, which, if done at all, must be done arbitrarily, for it fades out so gradually that no real demarkation exists. The same may be said of its eastern boundary. But assuming the plateau to extend northward to the base of the Tushar and eastward to the Sevier Plateau, the length would be about 50 miles and the breadth about 28 miles. The greater part of this area is covered with ancient eruptions resting upon Tertiary lacustrine beds. Around the southern and western sides of the plateau the sedimentary strata project several miles beyond the volcanic sheets and end abruptly in giant cliffs, facing the south and wert, and deeply scored by erosion. The western wall of the plateau is formed by the northward prolongation of the Hurricane fault, while the southern wall consists of cliffs of erosion without any known dislocation of great magnitude. These southern cliffs are the lingering remnants of Tertiary and Cretaceous beds, which once extended over the entire region to the southward beyond the Colorado, but have throughout Tertiary time receded by waste to their present boundary. The detailed description will begin at the northern portion. At the foot of the lofty summits which crown the southern end of the Tushar lies Dog Valley, inclosed south and west by rolling and somewhat rugged volcanic hills and by remnants of a great volcanic conglomerate. Similar hills are found to the eastward, and the whole tract is a center or focus of eruptions of the trachytic epoch. The cones and craters which may once have existed are no longer visible, having been wasted to a medley of hills by a period of decay which stretches far back towards middle Tertiary time. Soil and gravel, with a rich growth of wild grass and shrubbery, now mantle these degraded remnants, giving them a rather pleasant and gentle aspect. Yet the outcrops of volcanic sheets around the borders and away from the valley betray its history in spite of the effort of nature to hide it. East, west, and south the old floods are seen to radiate away for many miles from this center, spreading out and growing thinner as they were poured along over the ancient inequalities of the land. They also |