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Show HIIBRICANE AND TUSHAE FAULTS. 29 From the Grand Canon northward for 40 miles it is a nearly simple fault, though in some places it shows comminution of the rocks in the vicinity of the fault plane, and in a few places the beds on the thrown side are turned up. Along the southwestern base of the Markagunt the fracture becomes very complicated. The upper beds have been eroded backward from the fault plane on the lifted side of the fault, and the lower beds on that side have in several places been turned up with a sharp flexure and stand nearly verticalâ€"in one instance have been turned past the vertical. This movement seems to be exceptional, no other instance of the same kind having been seen anywhere. It is difficult to understand by what application of forces such a contortion could have been effected. The Carboniferous has been brought up by it so as to abut against the Tertiary on the thrown side of the fault, and right at the plane of shearing the displacement of the lower beds seems to be about 12,000 or 13,000 feet. But away from the fault plane the beds quickly come back to their normal position, with an uplift of about 4,000 feet. A few miles south of this point another equally abnormal displacement occurs. A small branch of the fault runs into the uplift and a huge block seems to have cracked off and rolled over, the beds opening with a V, and forming a valley of grand dimensions. About six miles north of the great upturn all trace of that peculiar flexure has vanished and the beds are neatly sheared. The Hurricane fault nowhere appears to take on the true monoclinal form. The length of this great displacement is probably more than 200 miles. The third great fault is that which lies at the eastern base of the Tu-shar. Most of the faults have their throws to the west, but the throw of the Tushar is to the east. It commences with two branches at the southeastern base of the range and the branches converge near the middle of its eastern flank They are obscure and difficult to locate exactly on account of their concealment by the alluvial debris, resulting from the waste of the ancient lava beds and the somewhat chaotic nature of the tract through which they run; for this tract is one of the old centers of eruption. But some well preserved beds of conglomerate turned up on the thrown side and matched with beds appearing above at last revealed them, and the discovery of a series of peculiar trachytic beds on both sides of the fault |
