OCR Text |
Show SEVIER FAULT. 31 thrown side and remain horizontal on the other. The beds, five miles from the fault on the thrown side, come back to horizontality at about the same levels which they occupy on the other side of the fault, Fig. 3. The trend of the fault at first is northeast. Ten miles from Pipe Spring it is a simple fault. Farther on, in Long Valley, it is " stepped" with two branches. Passing on to the base of the Paunsagunt at Upper Kanab the beds on the thrown side are flexed upward, while on the lifted side (east) they are horizontal. This form continues northward from Upper Kanab for about 13 miles, when branch faults appear on the thrown side and the fault is stepped and here and there somewhat comminuted, but with one predominant shear, forming the western wall of the Paunsagunt Plateau. These modifications disappear about 6 miles farther on, and the fault becomes simple with a diminished throw, the displacement opposite the village of Hillsdale not exceeding 800 feet. Beyond Hillsdale the throw is nearly uniform for about 10 miles and then increases again. The increase is slow but steady for the next 60 miles. Along the east side of Panquitch Valley it is very difficult to study, because it cuts the volcanic rocks, which are much confused, and here is one of the great eruptive centers. It is probably somewhat complicated, though the principal displacement is distinctly revealed in the great plateau wall on the east, and in the great ravines and chasms which cut across it and open into the valley below. Opposite Circle Valley the fault splits off a large piece from the Sevier Plateau by means of a branch which leaves the main displacement and then reunites with it. At East Fork Canon the thrown beds, consisting of volcanic conglomerate, are turned up monoclinally, but are sundered by the, fault at the summit, with a shear of 3,000 feet. A little north of this canon a branch diverges from the main displacement, running off into the Sevier Valley, where it rapidly dies out. The maximum displacement is apparently attained a few miles south of the Mormon village Monroe, and from that point northward it rather rapidly diminishes. Between Grlenwood and Salina the apparent shear has become zero. But the circumstances are remarkable. The fault from Monroe northward is a secondary displacement superposed upon an older one. The zero point of the fault is quickly succeeded in the same line by a resumption of the shear, but in the opposite |