The Muskeg or Prairie Formation is part of the Middle Devonian Elk Point Group of Western Canada. Muskeg rocks grade from marine shale and carbonate in northeastern British Columbia through anhydrite and salt to highly concentrated potassium salts in Saskatchewan. The same progression from less to more concentrated end members is repeated in vertical succession in six composite lithologic units. The cyclic succession of beds and their lateral and vertical facies relations provide a textbook example of an intracratonic salt basin, barred by prominent barrier reefs and fringed by reefoid banks and vast anhydrite platforms.

Large reserves of oil are trapped in pools arranged along the western and southern edge of the Muskeg salt. This association is too consistent to be accidental.

Growth patterns and distribution trends of porous carbonate and sandstone facies from Devonian to Cretaceous suggest that the rim of the salt basin was a persistent locus of epeirogenic differentiation. The regional tectonic trends were modified further by movement of salt and possibly salt solution, providing a variety of local structures where oil was pooled.

In northwestern Alberta Muskeg evaporites are directly involved in the pooling of oil as source rocks, as cap rocks, and as flank seals to prolific pinnacle reefs. Some reef sections are equivalent in age to Muskeg evaporites in the salt basin. Muskeg carbonates sandwiched between evaporites also produce oil.

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