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The Cretaceous Lewis Shale-Fox Hills-Lance Formations in southern Wyoming (1) were deposited during the final transgressive-regressive cycle of the Cretaceous western interior seaway (2). These formations comprise a third-order highstand systems tract (3) composed of several fourth-order lowstand-highstand cycles. One of these fourth-order cycles is well exposed in three outcrops — called Spine 1, Spine 2, and Rattlesnake Ridge — over a distance of 3.2 km (2 mi) (4). The strata within these outcrops are important for two reasons: 1) they provide good outcrop exposures of the Lewis Shale in an area of active exploration for gas, and 2) the Dad Sandstone Member of the Lewis Shale here is considered to be an excellent, scaled analog of delta-fed, mud-dominated, progradational, turbidite systems that are hydrocarbon-productive in areas such as the Gulf of Mexico and offshore west Africa.

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