Geologic History of Wyoming

The topographic expression we currently observe across Wyoming evolved over billions of years and resulted from a variety of natural geologic processes acting internally or externally on the earth’s surface. In addition to the mountain ranges, high plains, and sedimentary basins that span the state, the development of Wyoming’s vast energy resources and mineral deposits, as well as potential geologic hazards, can all be attributed to geological processes and structural deformation.

Explore the geologic evolution of Wyoming below to discover the timeline of significant events that shaped the land as well as a brief summary of the general geology of major uplifts and basins in the state. 

Wyoming's Geological Timeline

Read below to learn more about the geologic evolution of Wyoming. A geologic time scale is provided below for reference. The "Ma" heading on the time scale represents the term "mega-annum," which means a period of one million years. The "Ga" heading on the time scale represents the term "giga-annum," which means a period of one billion years.

Cenozoic (66 Million Ma to Present)

The Laramide orogeny began in Wyoming in the Late Cretaceous. The peak of deformation occurred during the Paleocene, and the orogenic event was completed by mid-Eocene. Erosion removed sediments from highlands and deposited them into surrounding basins, which subsided as the mountains rose. A period of volcanic activity occurred during the Cenozoic, depositing volcaniclastic rocks, flows, intrusive-volcanic bodies, and ash. The entire Rocky Mountain region underwent a period of significant uplift, and the Pleistocene Ice Age began. Today, there are still earthquakes in the state, suggesting continued crustal movement.

Mesozoic (252–66 Ma)

Deposition of red sediments continued throughout the Triassic period. The Jurassic period is marked by minor crustal uplift and transgressive/regressive sequences of the sea. Marine clay, mud, and sand were deposited, and marine fossils were widely preserved. During the periods when Wyoming was dominated by a continental environment, fluvial systems deposited clay, silt, and sand. Dinosaurs inhabited the land during the Jurassic and many world-renowned fossil remains have been discovered at sites across the state. In the Cretaceous, a seaway again covered most of the state. By the end of the Cretaceous, the Sevier orogeny was underway and the Overthrust Belt was developing. The end of the Mesozoic also marks the extinction of dinosaurs in the geologic record.

Paleozoic (541–252 Ma)

Cambrian and Ordovician deposits in Wyoming record subsidence of the land that resulted in westward transgression of the sea and deposition of marine sediments (gravel, sand, mud, limestone, and dolomite). The Silurian record is not well preserved in Wyoming and likely reflects a period of widespread erosion. Mountain-building events that commenced in the Pennsylvanian period uplifted the crust and eroded sediments, depositing them into adjacent, low-lying basins where an inland sea still covered the land. In the Permian, organic-rich marine sediments were deposited in the western seaways while nearshore tidal flat sediments accumulated in the central and eastern parts of the state, resulting in the thick sequences of red siltstone, shale, gypsum, and sandstones we see today.

Precambrian (4.6 Ga541 Ma)

The Precambrian history in Wyoming is best documented from studies in the Medicine Bow Mountains. Radioactive dating of rocks exposed at the surface indicates two igneous-intrusive events (2.7 billion years ago and 1.7 billion years ago). Additionally, the Medicine Bow Mountains have a thick metasedimentary cover containing fossilized cyanobacteria (stromatolites) which are as old as 1.7 billion years. The cyanobacteria are evidence of some of the first known life forms on earth. The Sherman Granite represents a younger Precambrian magmatic igneous-intrusive body and crops out along U.S. Interstate 80 in the vicinity of the Vedauwoo Recreation Area. Precambrian rocks are also exposed at the core of many uplifts in Wyoming.

geologic time scale
Geologic time scale. (Ma = mega-annum (a period of 1 million years))



Colby Schwaderer,