278 GEOLOGY OF THE HIGH PLATEAUS. 



latter debouched. The Fremont River, however, still maintains its course 

 in one of those old canons for a distance of 4 or 5 miles. It leaves the low 

 flats of the valley to enter the rising slopes of the Awapa and flows through 

 a rocky gorge which becomes four or five hundred feet deep. Thence it 

 emerges into the valley plain again and pursues its way to the foot of the 

 valley, where a salt marsh, covered with saline pools, has been built up by 

 the accumulation of fine silt. 



It is interesting to pursue this subject further and to view it in relation 

 to future instead of past time. The river leaves the valley through the 

 great gap between the mountain and the Aquarius, and the passage has 

 been named the Red Gate. Thence it flows off into the heart of the 

 Plateau Country, reaching the Colorado by a profound canon. Throughout 

 the greater part of this distance the river is a rapid stream and is slowly 

 sinking its channel. Its rapid descent begins half a mile beyond the point 

 where it crosses the great fault, and it is apparent that here, too, it is 

 lowering its bed; for old terraces of river gravel and loess are seen at 

 different levels within the Red Gate in an excellent state of preservation, 

 and the river has cut a broad and deep channel through them. It is only 

 a question of time how deep the channel may be cut, for where it leaves 

 Rabbit Valley the altitude is almost exactly 7,000 feet above sea-level, and 

 the junction of the river with the Colorado is less than 4,500 feet. Esti- 

 mating the course of the stream between the two points at 100 miles, the 

 average descent is not far from 25 feet to the mile, which is about the same 

 fall as prevails in nearly all the tributaries of the Colorado in this part of 

 the country. All of them are evidently corrading their beds. Here and 

 there local flood plains are formed, occurring along stretches of the streams 

 where the fall is slight ; but such flood plains are merely temporary in the 

 secular life of the river. They are succeeded by rapids which are grad- 

 ually eating their way backwards, and in a brief period the stretches of still 

 water will become rapids in turn. In time, then, the Fremont River will cut 

 down its channel at the outlet of Rabbit Valley unless the fault at the Red 

 Gate increases its throw. In the absence of such increase in the fault the 

 stream will ultimately carry back the excavating process into the valley 

 and the extensive alluvial beds will be gradually attacked and eroded away. 



