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 Torm a broad platform or terrace skirting the south- 

 eastern flank, and ending in a beautifully sculptured cliff about 600 feet 

 high, eminently characteristic of the formation. The architecture is repre- 

 sented in Heliotype X, but the colors are such as no pigments can 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 down- 

 wards 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 im- 

 mense 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 tribu- 

 taries 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 Gate 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. 



