Mountains and Basins

Mountains and Basins

Wyoming's Uplifts and Basins

Hover over a mountain or basin on the map below for more information on the general geology of the area.

Generalized Wyoming cross section

Key Mountain-Building Events

Although several orogenic (mountain-building) events have played a role in shaping the geology of state, two main events are most commonly referenced when considering Wyoming geology, the Sevier and Laramide orogenies. Learn more about these events below.

Sevier Orogeny (140-50 Ma)

As part of the Cordilleran Thrust Belt, which extends from Mexico to northern Alaska, the Sevier orogeny occurred in Jurassic to Eocene time, approximately 140–50 million years ago when the Farallon oceanic plate subducted beneath the continental crust of North America near present-day California. Compressive stresses related to collision of the plates resulted in crustal thickening and mountain building in parts of Nevada, Utah, Idaho, and Wyoming. The north-south trending mountain ranges in western Wyoming are referred to as the Thrust Belt, the Overthrust Belt, or the fold and thrust belt, and are Sevier structures. Classic Sevier structures are west-dipping, east-vergent thrust faults that displace sedimentary rocks above the crystalline basement. Because these thrusts do not involve basement rocks, they are referred to as “thin-skinned.” Western Wyoming mountain ranges that comprise the Thrust Belt include the Snake River, Wyoming, Hoback, Salt River, Tunp, and Sublette ranges.

Laramide Orogeny (70-35 Ma)

The Laramide orogeny is a significant mountain-building event that occurred synchronously with the Sevier orogeny during the first 20 million years of its duration (70–35 million years ago). Similar to the Sevier mountain-building event, the Laramide orogeny is thought to be caused by horizontal compression from subduction of the Farallon Plate beneath the North American Plate. Laramide structures differ from Sevier deformation in that Laramide faults displace crystalline basement rocks as well as sedimentary rocks. This is referred to as “thick-skinned” deformation. Laramide deformation is unique because it occurred farther inland on the North American Plate rather than at the plate boundary, which is more typical in convergent margin settings. One hypothesis for inland deformation is that the angle in which the Farallon Plate subducted became shallower, causing crustal thickening in the direction of subduction.

Deformational Styles

The cross section below highlights the difference between Sevier-style and Laramide deformation. Sevier-style thrust faulting is confined to sedimentary rocks above the Precambrian basement (i.e. thin-skinned). Laramide structures offset Precambrian basement rocks (i.e. thick-skinned).

deformation cross section
Sevier-style and Laramide-style deformation cross section



Colby Schwaderer,