OCR Text |
Show BEAE YALLEY. 191 about 1,400 feet. It cannot be regarded as a part of the Markagunt, but occupies an intermediate position between that plateau and the Tushar. It is interesting chiefly as being the locality from which emanated a large portion of the lavas of the trachytic eruptive epoch. Probably it was the scene of eruptions of the first epoch also, though the lavas which it may have there poured forth are deeply buried beneath the great extravasated masses of the second period, and are revealed only in the fragments of andesite which are seen in the older conglomerates and by the lower beds at the base of the Tushar, which are brought up to daylight by the fault at its base. Crossing the southern rim of Dog Valley we descend into another valley of a little lower altitude, called Bear Valley. The divide between the two consists of a low range of hills, which are the degraded remnants of old volcanic piles which were once, no doubt, of imposing magnitude, giving vent to the huge sheets of lava which diverge from them, but are now reduced to mere hills and discrete masses of dolerite and basalt. Reaching the bottom of Bear Valley, we find a smooth, park-like inclosure of ample dimensions, with high hills of trachyte on the east and the brilliant rosy red of the Eocene (Bitter Creek) on the west. It has already been stated that the Markagunt has a fringe or border of sedimentary rocks upon its western and southern sides, and this border is from 2 to 6 miles in width. In other words, the volcanic beds which cover its central and eastern portions do not extend to the western and southern margins of the uplift. Bear Valley lies at the foot of a broken crest which is formed by the sudden termination of these eruptive masses. This boundary is a very irregular one, having westward projections and eastward recesses. But it is necessary to keep in mind one important relation. The vents stood near this western margin. The main flow of the erupted materials was towards the east, in which direction they extended probably as far as the Sevier Plateau, or until they are lost beneath more recent sub-aerial accumulations. Towards the west their progress was arrested by the rising slope of the country, and they do not appear to have extended more than a very few miles in that direction. Then, as now, the face of the country sloped downward from west to east, though the gradient was considerably |