The Chester Series of the Mississippian System covers all or part of 12 of the counties that comprise extreme southwestern Kansas. The erosional surface on which sediments of Chester age were deposited was an extremely rough one, representing a major unconformity. Significant commercial oil fields have been found in sandstones of Chester age in this area. Commercial oil accumulated in highly lenticular sandstones. This oil accumulation is mainly stratigraphic Chester sediments change thickness abruptly in the area that was studied. The Chester seas generally were transgressive with several periods of quiescence. Several facies are recognized, including the sandstone facies.

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