Laramie Basin Geology

The Laramie Basin, in southeast Wyoming, is a complexly downfolded Laramide basin. It trends north-south and is approximately 80 km (50 mi) long by 50 km (31 mi) wide. The Laramie Basin is bounded by the Medicine Bow Mountains on the west, Hanna Basin on the northwest, Shirley Mountains on the north, and Laramie Mountains on the east.

The Laramie Basin formed during the Laramide orogeny, from the Late Cretaceous to middle Paleocene. The pre-Laramide sedimentary rocks along the flanks of the basement-cored Medicine Bow Mountains have been extensively folded and faulted. Less deformation is observed on the eastern margin where these same sedimentary rocks are tilted and rest unconformably on the 1,432–1,436 Ma Laramie Anorthosite Complex (Frost and others, 2013) or the 1,433 Ma Sherman Granite (Frost and others, 1999) further to the south.

Similar to in other Laramide basins, oil and gas in the Laramie Basin is commonly found in asymmetric anticlinal traps that occur in the northern half of the basin. One exception is a stratigraphic trap in the Muddy Sandstone of the Big Hollow field (Pritchett, 1985). Oil-producing formations in the basin include the Pennsylvanian Tensleep Sandstone, the Lower Cretaceous Muddy Sandstone, and the Lakota (Cloverly) Formation. Minor oil production has also come from the Jurassic Sundance and Upper Cretaceous Wall Creek formations. The most productive natural gas reservoirs in the Laramie Basin are the Lakota (Cloverly) Formation and Muddy Sandstone in the Rock River field, and the Shannon Sandstone Member of the Upper Cretaceous Cody Shale in the Dutton Creek field.


Quealy field in the western Laramie Basin was the first field in the Rocky Mountain region to be discovered using seismic methods. The California Company used reflection seismic surveys to delineate the Quealy Dome anticline and drilled the first productive well in Quealy field in 1934 (WSGS oil and gas map). Hydrocarbon exploration and development in the Laramie Basin has since been limited compared to most of Wyoming’s other Laramide basins. While oil has been the primary target in the Laramie Basin, eight of the ten currently active fields have also produced gas (WOGCC, 2024).

Future Development

No new wells have been drilled in the Laramie Basin since 2014 (WOGCC, 2024). It remains to be seen if and when the unconventional plays being targeted in other Wyoming basins will also be developed in the Laramie Basin.

Casper Formation
Casper Formation, southwestern Laramie Basin. [Credit: WSGS]



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