25 



COLORADO AND 



NEW MEXICO ROCKIES 



COLORADO ROCKIES 



Geography 



Figure 25.2 shows the principal features of geologic interest in Colorado, 

 and on it the above-mentioned belt of Laramide deformation may be 

 identified. The Front Range is the largest and highest of any in the 

 Rockies of the western United States. The most rugged mountains are 

 in the central part with a number of peaks exceeding 14,000 feet in ele\ a- 

 tion. The western flank slopes steeply away from the crest of the range, 

 but the eastern slope is characterized by broad, dissected, benchlike 

 erosion surfaces that descend in steps to the Great Plains. 



A series of valleys or basins occupy a central position to the flanking 

 ranges on east and west, namely, North Park, Middle Park, South Park, 

 and Huerfano Park. The San Luis Valley lies west of the Sangre de Cristo 

 Range and continues the basins in offset fashion into New Mexico. 



The Colorado Plateau extends across western Colorado to the Park 

 and Sawatch ranges and is generally considered to include the Piceanoe 

 basin, the White River uplift, and the Uneompahgre uplift. An extensive 

 volcanic field obscures much of the Laramide geology between the Needle 

 Mountains of the San Juans and the Sawatch and Sangre de Cristo 

 ranges. 



The Denver, Trinidad, and Raton basins on the east of the Colorado 

 Rockies are Laramide downwarps. 



J EXTENT OF LARAMIDE DEFORMATION 



! 



Most geologists regard the high relief features in central Colorado, 

 composed principally of the Park, Front, Sawatch, Wet, and Sangre de 



r Cristo ranges, as the Laramide structures of the state. The belt is about 

 80 miles wide and extends in a north-south direction. See Fig. 25.1. It 

 continues southward to southern New Mexico where it joins the Laramide 

 belts of Mexico and southern Arizona. 



An arm extends southwestward from the Sawatch Range to and includ- 

 ing the San Juan Mountains. 



Relation of Laramide Rockies to Ancestral Rockies 



The Colorado Range of the Ancestral Rockies has been described on 

 previous pages. It was gradually overlapped from the east and west and 

 nearly buried by late Cretaceous time. During the Laramide unrest 

 the modern Front Range rose approximately along the eastern half of the 

 ancestral range, and the basins of the Middle and North parks and the 

 Park Range appeared approximately along the western half. See Figs. 

 25.3 and 25.4 



The ancestral Central Colorado basin with its thick fill of Pennsylvania!! 

 and Permian red beds and evaporites, and also an appreciable thickness 



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