Upper Minnelusa sandstone reservoirs of the Powder River basin produce oil from structural and unconformity traps. This sandstone probably is Wolfcampian in age and was deposited in shallow-neritic to littoral environments which characterized eastern Wyoming. Post-Wolfcampian erosion left remnants of Minnelusa sandstone beds which were covered by red shales and evaporites of younger Permian age.

Minnelusa oil fields of the northeastern Powder River basin, such as Raven Creek and Halverson, are mainly unconformity traps. Updip truncation of the Minnelusa is reflected by abrupt thickening of the overlying Opeche red shale, basal member of the Goose Egg Formation. Minnelusa fields of the western Powder River basin, such as North Fork, are largely structural traps, but post-Wolfcampian truncation may account for as much as half of the closure. In these fields Minnelusa sandstone is preserved on top of structures, and truncation on the flanks is reflected by abrupt thickening of the entire overlying Goose Egg section.

More than 100 million barrels of oil has been found in the upper Minnelusa. As productive trends are revealed by drilling, more oil will be discovered in structural, unconformity, and combination traps throughout the Powder River basin.

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