CORRELATION OF FORMATIONS 475 



folding, presumably of several epochs, undoubtedly adds much to the 

 complexity of the relations. 



Newberry's section. — The Red beds of the Grand River valley and can- 

 yon, for some distance below the mouth of the Dolores, may be assumed 

 to correspond in general to the development possessed in the Dolores 

 valley. It is only from 25 to 50 miles west from Paradox valley to the 

 region where Newberry made, in 1859, a section in the " Canyon Colorado," 

 which enters Grand river from the east a few miles above its junction 

 with Green river. In Newberry's often cited "Generalized section of 

 the valley of the Colorado " (33, page 99) (in which it should be noted 

 he does not refer to the " Rio Colorado Grande," as the Colorado river is 

 termed on his map) some 1,726 feet of beds are referred to the Trias. 

 Below this section some fossiliferous Carboniferous (Pennsylvanian) 

 strata and above them Jurassic beds with large saurian bones and fossil 

 wood, which latter undoubtedly belong to the McElmo formation. 



It seems to me that the three upper divisions of Newberry's Trias, 

 aggregating 970 feet in thickness, belong to the Jurassic, and possibly 

 represent the three divisions of the La Plata formation, corresponding 

 to those occurring in the Dolores valley. Nothing appears in Newberry's 

 section which can be definitely correlated with the "saurian conglomer- 

 ate " zone of the Dolores formation, but the suspicion may be entertained 

 that the equivalent of the latter is described in number 11 of his section, 

 embracing 92 feet of " greenish-gray micaceous conglomerate and gray 

 sandstone, separated by red or purple shales." If this is correct, there are 

 514 feet of red sandstones below, which may represent the Cutler forma- 

 tion. 



FORMATIONS OF THE LOWER SAN JUAN VALLEY 



In general. — From the summits of the La Plata or Rico mountains 

 one may look westward far out over the plain, the monotony of which 

 is relieved here and there by isolated mesas, remnants of older plateaus. 

 In the early morning or near sunset one can often get a glimpse of the 

 precipitous scarps and the gigantic towers and pinnacles of San Juan 

 valley, 100 miles away, which stand out with a rosy gleam or in con- 

 trasting dark shadow, and give a faint suggestion of the wonderland 

 lying just beyond the limit of vision. Going toward this distant valley 

 of remarkable erosional forms one passes over the plain called the Monte- 

 zuma valley, underlain by the Dakota sandstone, and at about 25 miles 

 from the La Plata slopes enters the drainage of McElmo creek. This 

 stream unites with the San Juan river where it turns westward to the 

 Colorado after its long detour in New Mexico and Arizona. The can- 

 yons of the various branches of the McElmo are cut in the Jurassic beds 

 and the name has been given to the upper formation described in pre- 



