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Show 282 GEOLOGY OF THE HIGH PLATEAUS. cane fault, 150 miles to the southwest. The shales also present the same striking and constant appearance as if in all that interval not a layer or line had lost its identity. At the base of the mountain, upon the southern side, the Shinarump shales form a broad platform or terrace skirting the southeastern flank, and ending in a beautifully sculptured cliff about 600 feet high, eminently characteristic .of the formation. The architecture is represented in Heliotype X, but the colors are such as no pigments qan portray. They are deep, rich, and variegated, and so luminous are they, that light seems to glow or shine out of the rock rather than to be reflected from it. The Red Gate has already been alluded to as the passage by which the Fremont River leaves Rabbit Valley and flows off into the heart of the Plateau Country. As we approach it from the west the flaming red of the Trias is seen reaching out southward from Thousand Lake Mountain in a rocky wall which has been breached by the river. These beds curve downwards on the south side of the gate and disappear beneath the spurs of the Aquarius. The great fault along which Thousand Lake Mountain has been upheaved continues southward across this passage, cutting into the mass of the Aquarius. The downward flexure of the Trias is simply the effect of diminished uplift on the south side of the gate. The passage itself has been cut by the river, which has occupied its present locus for an immense period, which may reach back as far as Miocene time. Some changes may have occurred in its course through the repeated outflows of lava across and into its valley. But there are independent considerations which lead to the conclusion that the Fremont River is one of the more ancient tributaries of the Colorado, born with the country itself far back in Eocene time, though its upper branches may have been much modified by the violent changes accompanying the great volcanic activity of the Middle Tertiary. Beyond the Red Grate the relations of the river to the structural features of the region through which it flows, and also to the imposed sculpture of the country, are such as to compel the conviction that the river must antedate the Tertiary deformations of the strata which are there found, and also antedate the great erosion of the Plateau Province. Through all those vast changes by displacement and erosion the river has ever maintained its thoroughfare. The passage through the Red Gate is part and parcel of the same history. i |
