454 CROSS AND HOWE — RED BEDS OF SOUTHWESTERN COLORADO 



At Ouray the Uncompahgre issues from a deep gorge cut in Algonkian 

 quartzites and slates, crosses a fault along which the lowest Paleozoics 

 are steeply upturned against the Algonkian series, and thence flows 

 northward in the general dip line, exhibiting in its banks the entire 

 sequence of beds, as high as the coal-bearing portion of the Cretaceous* 

 Just as the river crosses the fault mentioned it is joined on the west by 

 Canyon creek, an important tributary, and by Oak creek, a smaller one. 

 On the eastern side, opposite Canyon creek, is a splendid glacial cirque, 

 called " The Amphitheater/' the town of Ouray being situated on the 

 alluvial fans deposited by the streams from that deep recess. 



The northern walls of Canyon creek and of the Amphitheater come 

 close together immediately below Ouray, and the Uncompahgre once 

 more flows in a canyon for 2 miles, the walls rising abruptly for 3,000 

 feet and exhibiting fine sections of the sediments as high as the Mancos 

 Cretaceous shales, above which come the volcanic tuffs. These cliffs, 

 and especially those facing the town of Ouray, are already celebrated 

 among tourists for their rugged forms and attractive coloring and must 

 in future be classic ground to the student of Colorado geology, because 

 in them is so clearly revealed one of the most important unconformities 

 of the province, evidence which will be of great assistance in solving a 

 long debated point in Rocky Mountain stratigraphy. 



It was stated by R. C. Hills in 1882 (21) that the fossiliferous Triassic 

 horizon observed by him on the western and southern slopes of the 

 San Juan was absent in the Uncompahgre section. This is an error? 

 however, as the study of the Ouray quadrangle by the authors during 

 the season of 1904 showed that the Dolores Triassic formation, though 

 very thin, is present in the Uncompahgre valley, and is there separated 

 stratigraphically from the underlying Red beds by a pronounced angular 

 unconformity. This important stratigraphic relation has hitherto escaped 

 recognition, apparently through the difficulty of reaching the places where 

 it is most clearly demonstrable, and owing to the apparent conformity 

 within the Red beds as they dip beneath the valley. The angular uncon- 

 formity to be described is, however, visible for some miles from certain 

 directions, and only the circumstance that no detailed work has ever 

 before been done in the Ouray district can explain the delay in recog- 

 nizing the relations here under discussion. 



The views of plates 82 to 85, with the explanations afforded by the 

 accompanying diagrams, show perhaps more clearly than word pictures 

 can do the position of the unconformity and its pronounced character. 

 Plate 82 shows how plainly the unconformity stands out, as seen from 

 the northern slope of Canyon creek at a distance of 5 miles. The 

 dark wedge-like mass in the cliffs near the Amphitheater consists of 



