PEALE.] AREA A PARADOX VALLEY, ETC. 169 



to the northwest aod southeast at right angles to the course of the 

 river, has been named Paradox Yalley. The beds on both sides of the 

 valley present their basset edges toward the axis of the valley and dip 

 gently away from it to the southwest and to the northeast. It would 

 appear, therefore, to be a simple anticlinal axis with the centre removed. 

 The erosion of the strata has greatly obscured the relations of the dif- 

 ferent beds. The blufts on the southwest are lower than those on the 

 northeast, and show no beds lower than the Jurassic variegated shales, 

 while the opposite ones show a considerable thickness of the underlying 

 red sandstones and shales that we have been accustomed to refer to the 

 Trias. If, therefore, this valley be a simple anticlinal, it must occupy 

 a position west of the axis. I am inclined to believe that it — the fold — is 

 not simple, but analogous to that of Gypsum Valley, *. e., there is a fold 

 with a fault to the eastward, along the foot of the bluffs on that side. 

 Crossing to the southeast to the synclinal basin on Basin Creek, we find 

 evidences of faulting on a direct line with the bluffs. The fault of the 

 west side of Sindbad's Valley (see p. 63, Eeport U. S. Geol. Survey for 

 1875) is also on the same line. The prevailing formation in the valley 

 is the Trias *? covered in most places with drift. The latter increases 

 toward the north. The bluffs on the northeast, as we go north, are in two 

 steps, the upper being of Dakota sandstone, which slopes to the San 

 Miguel River. The lower step has Jurassic shales capping the red sand- 

 stone. North of the Dolores, the Eed Beds prevail and Upper Carbonif- 

 erous beds outcrop at the base of the cliffs. Owing to the limited time, 

 this portion of the valley was not visited, 



SAN MIGUEL PLATEAU. 



The San Miguel Plateau calls simply for a mention here, as the re- 

 ports for 1875 refer to it so frequently. We crossed it on the trail that 

 leads from the Uncompahgre agency to the Navajo Indian country. 



The elevation of the plateau near the mountains is about 8,000 feet, 

 and here pines are found. Near the mouth of the San Miguel the ele- 

 vation is about 6,000 feet, and the surface covered generally with sage- 

 brush. All the streams are in canons from 800 to 1,000 feet below the 

 surface, with but little bottom-land. The Dakota sandstones form the 

 surface rock, but that higher beds once prevailed over the entire area 

 is evident from the remnants of Colorado shales that are now found at 

 several localities. The largest area of shales is found between the San 

 Miguel Eiver and Tabeguache Creek, occupying a synclinal depression. 

 The areas of shales are indicated on the map (Plate VIII). 



