THE BUILDING OF TEE COLORADO ROCKIES 153 



tana group. ^ The exact extent of this diastrophic movement has 

 not yet been satisfactorily determined for the Colorado region, 

 principally for the reason that contacts between the Cretaceous and 

 early Eocene within the folded portion of the range are few and 

 very unsatisfactory, owing to the great amount of erosion which 

 has taken place there. Folded or faulted Cretaceous beds overlain 

 by less disturbed early Eocene strata are not found at many places 

 in Colorado. In Wyoming, however, there are numerous sections 

 in which the Adaville formation (upper Montana and lower 

 Laramie) shows profound folding and faulting followed by extensive 

 erosion before the deposition of the Evanston (early Eocene) 

 beds, which lie in strong discord across the truncated edges of the 

 Mesozoic strata.- 



In Colorado the Laramide upfolding of the Rockies resulted in 

 a rapid erosion of the newly risen mountains and the accumulation 

 of the Dawson arkose and the Arapahoe conglomerate near Colo- 

 rado Springs and Denver, and the development of the Raton 

 formation farther south. Some idea of the extent of the upfolding 

 may perhaps be obtained from the amount of erosion which immedi- 

 ately followed. Cross has estimated that post-Laramie erosion 

 had already, in Arapahoe times, removed from portions of the 

 folded belt west of Denver the great total of 14,000 feet of strata, 

 since pebbles derived from various geological horizons down as 

 tar as the Trias are found in the Arapahoe beds.^ In the same way 

 Lee has estimated that the conglomerate at the base of the Raton 

 iormation in southern Colorado is stratigraphically more than 

 18,000 feet above the crystalhne and metamorphic rocks that 

 iurnished most of the pebbles found in it."" Lee, however, recognizes 



'Willis T. Lee and F. H. Knowlton, "Geology and Paleontology of the Raton 

 Mesa and Other Regions in Colorado and New Mexico," U.S. Geol. Survey, Prof. 

 Paper loi (191 7), p. 64. 



^ A. C. Veatch and A. R. Schultz, " Geography and Geology of a Portion of 

 Southwestern Wyoming," U.S. Geol. Survey, Prof. Paper 56 (1907), PI. IV; A. R. 

 Schultz, "Geology and Geography of a Portion of Lincoln County, Wyoming," 

 U.S. Geol. Survey, Bull. 543 (1914), PI. III. 



J Whitman Cross, "Geology of the Denver B asin in Colorado," U.S. Geol. 

 Survey, Monograph 27 (1896), p. 207. 



■t W. T. Lee, ^7.5. Geol. Survey, Prof. Paper loi (1917), p. 59. 



