22 



p. B. KING 



characteristic examples of which may be seen in the northern Rocky 

 Mountains of western Alberta and northwestern Montana, and in 

 the central Rocky Mountains of western Wyoming and southeastern 

 Idaho. Farther south they have been obscured by later structures 

 of the Basin and Range province. 



From central Montana southward, Laramide deformation ad- 

 vanced well beyond the miogeosynclinal belt, disturbing part of what 

 had previously been the foreland, or border of the stable continental 



I I I I L. 



.10 



20 Miles 



Fig. 6. Diagram of a typical mountain uplift in Southern Rocky 

 Mountains. The example chosen is the Uinta Mountains of northeastern 

 Utah. The block in the background shows the feature without erosion of 

 the uplifted strata; that in the foreground the present topography. 

 (After Powell, 1876.) a, Pre-Cambrian rocks (here, sedimentary strata; 

 in other uplifts of Rocky Mountains, generally plutonic and meta- 

 morphic rocks), b, Paleozoic strata, c, Mesozoic strata, d, Tertiary strata. 



interior, and raised the central and southern Rocky Mountains of 

 Wyoming, Colorado, and adjacent states. Here, the sedimentary 

 cover was mainly thinner than in the miogeosyncline, and deforma- 

 tion created structures of a different style — broad-backed ranges of 

 diverse trend and spacing, in which Precambrian basement rocks 

 were so uplifted along the cores as to be uncovered by erosion, the 

 ranges being separated by broad basins (Fig. 6). 



Many of these structures were newly born during the Laramide 

 orogeny, but in the southern Rocky Mountains of Colorado and New 

 Mexico they were guided by structures of the "ancestral Rocky 

 Mountains" already referred to. Here, some of the Laramide ranges 

 nearly correspond to uplifts that formed in late Paleozoic time, 



