The Devonian System of North Dakota consists of rocks of Middle and Upper Devonian age. The Middle Devonian is represented in ascending order by the Winnipegosis, Prairie, and Dawson Bay Formations and the lower part of the Souris River Formation. The Upper Devonian is represented by the upper part of the Souris River Formation, the Duperow, and Three Forks Formations. These formations represent a total Devonian thickness of about 650 feet in south-central North Dakota, approximately 1,400 feet in the north-central North Dakota and about 800 feet in the southwestern part of the state. These units are dominantly carbonate rocks, the principal exceptions being the Three Forks shale and the evaporites of the Prairie Formation.

Though there is no Devonian production in these

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areas, the conditions necessary for accumulation are present and the Devonian formations that produce elsewhere in the Williston basin extend into these areas. In south-central North Dakota, conditions necessary for stratigraphic traps are present where the Devonian Duperow and Birdbear formations have been truncated by erosion and are unconformably overlain by an updip seal in the form of lower Mississippian shale.

In north-central North Dakota (southwestern Botineau County) conditions necessary for structural traps are present. In the 1½ miles between the Cardinal Keeler (NW., NW., sec. 1, T. 159 N., R. 82 W.) and the California Blanche Thompson (SW., SE., sec. 31, T. 160 N., R. 81 W.) removal of salt by solution from the Prairie Formation has resulted in collapse of the overlying sediments, creating a reversal in dip. It is probable that this is not an isolated situation along the edge of the salt and potentially extensive development of traps is indicated.

In southwestern North Dakota, Devonian sedimentation was influenced by the structure of the Cedar Creek anticline, causing the Winnipegosis, Prairie, Dawson Bay, and Souris River Formations to wedge out southwestward by non-deposition. The Duperow Formation is extensive, though thinned by erosion over the North Dakota part of the Cedar Creek anticline, and the overlying Birdbear and Three Forks formations have been removed by erosion. A thin shale, thought to be Mississippian in age, overlies these truncated formations. These conditions suggest that Devonian production from extensive stratigraphic traps may be found along the northeastern flanks of the Cedar Creek anticline in North Dakota.

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