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Show 1 0 UNDERGROUND WATER IN" VALLEYS OF UTAH. Traverse Mountains are largely composed of younger lavas, which conceal the rocks upon which they lie. In the " naiTows " where Jordan River flows through the Traverse Mountains, practically horizontal Pleistocene gravels, which form the great embankment at the point of the mountain, are unconformably underlain near the river level by fine- textured sediments that dip southeastward at an angle of 40°. The lower part of these sediments consists of light calcareous clay and the upper part of fine sand and gravel. No fossils were found, but the marked unconformity and the character of the material suggest that the age of the lower deposits is Tertiary. East of Utah Lake the great Wasatch fault is impressively shown by the remarkable alignment of the base of the mountains extending from Spanish Fork Canyon to the Traverse Mountains in an approximately straight line, and by the abrupt rise of the mountains above the broad valley. Second and third lines of faulting, lying parallel to the main fault and east of it, are suggested by the topography, which rises steplike, with two intervening treads between the ascents, to the top of the main ridge, and by the unusual thickness of limestone exposed, which apparently requires repetition by faulting for the explanation of its occurrence. In this part of the range a disturbed belt of rocks with prevailing steep westerly dips occurs along the western base of the mountains, beyond which the strata dip eastward at low angles and the summits of the main ridge are capped by limestone lying almost flat. The streams that cross the mountains, therefore, flow transversely to the strike of the rocks, in marked contrast to the creeks farther north, whose courses lie approximately parallel to the strike. Excellent sections can be measured along the canyons, but very little detailed work has yet been done. The rocks in general are quartzite and limestone of Carboniferous age, but locally Cambrian sediments also occur. In Rock Creek Canyon, east of Pr'ovo, in the lower end of the gorge, the rocks are much disturbed and are complexly folded. Here a considerable thickness of white quartzite outcrops, overlain by a great mass of limestone. In a thin bed near the base of the limestone G. H. Girty obtained a few Cambrian fossils, and about 600 feet above, in massive gray limestone, the beds being apparently conformable, he found Lower Carboniferous fossils. South of Hobble Creek easterly dips prevail from the base of the mountains as far as Spanish Fork, beyond which the range has been very little studied. It trends southwest-ward and terminates at Mount Nebo, the main mass of which is composed of steeply west-dipping limestone and subordinate quartzite of upper Carboniferous age. The highland farther south consists of a series of plateaus, which are underlain by low- lying Mesozoic and Tertiary rocks. The highlands that border the valleys of Jordan River and Utah Lake on the west are for the most part composed of the same rocks that occur in the Wasatch Mountains, but the structural relations are completely hidden by the deep filling of the intervening valleys. The Oquirrh Range is composed mainly of Carboniferous limestones and quartzites, which, in the southern part of the mountains, are folded into two parallel anticlines with an intervening syncline. The axes of folding are obliquely transverse to the topography, the range extending in a north- south direction while the structural trend is northwestward. The structure of the northern part of the mountains is little known, but the range is probably terminated by a fault. Rocks of Cambrian age are exposed locally by a fault in the vicinity of Mercur, and igneous rocks, both extrusive and intrusive, also occur. The intrusive rocks include both acidic and basic porphyries, which are conspicuous in the vicinity of the mining camps of Bingham and Mercur; the extrusive rocks, largely andes-itic, occur principally along the eastern base of the range and in the Traverse Mountains. The Lake Mountains, or Pelican Hills, west of Utah Lake, are composed of Carbonif-erous limestones and quartzites which constitute a low synclinal fold, and are separated from the Traverse Mountains by a narrow strip of Pleistocene deposits. A line of hills, |