20 P. B. KING 



Existence during this time of lands farther west, along the Pacific 

 border, has been stoutly maintained by various protagonists, but 

 evidence for such lands seems to have little substance. 



Sedimentation East of Nevadan Belt 



During Cretaceous time, especially during its latter half, a great 

 seaway extended along the eastern side of the Cordilleran region, 

 from the Gulf of Mexico to the Arctic Ocean (Fig. 4). In mid-latitude 

 in the United States its deposits were spread eastward into the con- 

 tinental interior as far as Kansas and Iowa and westward into the 

 Cordilleran region as far as central Utah. 



The eastern deposits were shallow-water shales and chalks of no 

 great thickness, but westward near the front of the Rocky Moun- 

 tains these pass into a dominantly shaly mass about 2 miles thick. 

 Beyond, wedges of sandstone appear in the shales and thicken west- 

 ward, with interbedded layers of coal that formed in swamps and 

 floodplains along the edge of the seaway. The westernmost preserved 

 Cretaceous rocks, near the west edge of the present Colorado 

 Plateau, are nearly 4 miles thick and are dominantly of continental 

 origin; they include coarse conglomerates that formed as piedmont 

 deposits adjacent to mountainous lands (Spieker, 1949, pp. 60-68). 



The source of these coarse, land-laid beds was clearly to the 

 west in the area of the present Great Basin (Fig. 4). The land barrier 

 that existed there during late Paleozoic and early Mesozoic time was 

 evidently enlarged eastward during Cretaceous time to include the 

 former miogeosynclinal area. This enlargement was the result of 

 folding and faulting, rather than of mere upwarp, and produced a 

 surface of varied relief that was rapidly eroded. 



Deformation of Miogeosyncline and Foreland 



During latest Cretaceous and Paleocene times, orogeny progressed 

 into the eastern part of the Cordillera, deforming the rocks of the 

 Colorado Plateau and Rocky Mountains as far as the Great Plains 

 (Fig. 5). This deformation, which completed the orogenic phase of 

 Cordilleran evolution, has been termed the Lar amide oroge?iy. It has 

 commonly been thought of as distinct, both in place and time, from 

 the Nevadan orogeny, but such distinctions are between end mem- 

 bers of a continuing sequence of deformation. Deformation began 

 earliest toward the west, then expanded across the miogeosynclinal 



