Osterwald and Dean reported in 1961 that The Cordilleran foreland is one of the major tectonic units of western North America. It includes the area between the Cordilleran geanticline and the interior platform and extends from the southern margin of the Colorado Plateau to the Rocky Mountain foothills in south-central Canada. Within the foreland a series of simple anticlinal mountains alternates with broad asymmetric basins. Most of the surface structures, including flexures and high-angle normal and reverse faults, are the result of recurrent vertical movements of blocks in the Precambrian basement rocks.
For convenience of description, the foreland is subdivided into 15 large tectonic units:
1. the Williston or Dakota basin;
2. the central Dakota terrace;
3. the Black Hills uplift;
4. the Lake Basin fault zone, Cat Creek fault zone, and Blood Creek syncline;
5. the Bighorn Basin, Bighorn Mountains-Pryor Mountains uplift, and Powder River Basin;
6. the Chadron arch uplift;
7. the Absaroka Mountains uplift;
8. the Owl Creek Mountains uplift, Wind River Basin, Sweetwater arch uplift and northern Laramie Mountains uplift;
9. the Wind River Mountains uplift;
10. the Green River basin and Rock Springs uplift;
11. the Uinta Mountains uplift;
12. the Great Divide Basin, Washakie basin, and uplift and basin complex;
13. the Sand Wash basin, Axial Basin uplift, and White River uplift;
14. Front Range-Park Range-southern Laramie Mountains uplift; and
15. the Denver basin and Hartville uplift.
Within the 15 tectonic units, uranium deposits can be related to the following large-scale structural environments:
a) crests of large-scale anticlines;
b) troughs of major basins;
c) flanks of large-scale uplifts where smaller structures are arranged in echelon;
d) flanks of large-scale uplifts where subordinate structures are parallel to the major structure;
e) conjunctions of major structures where trends intersect or merge with loss of identity of one or all trends and without an associated pattern of smaller scale structures;
(f) conjunctions of major structures where trends intersect or merge with loss of identity of one or all trends and where subordinate structures are parallel to or in echelon with the trend of one or all major structures.
Many uranium deposits can be more closely related by second-order discrimination to small- to intermediate-scale structures. Repetitions of the patterns to which known deposits are related may provide clues to areas containing presently unknown deposits.
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