The Oriskany (Ridgeley) Sandstone, Lower Devonian (Deerpark Stage), is one of the major deep gas producers in the central Appalachian basin. It is most productive in the southern tier of New York, western Pennsylvania, West Virginia, eastern Ohio, and to a lesser extent, in westernmost Maryland and northwestern Virginia.

Typically, the Oriskany is a calcareous quartzarenite with a distinctive megascopic fauna. Locally the Oriskany is orthoquartzitic, and in places conglomeratic. In outcrop, leaching of the calcareous components of the Oriskany produces a more friable, biomoldic quartzarenite. In the subsurface, the formation is usually tightly cemented by carbonate.

The Oriskany is a sheet sand that reaches a maximum thickness of over 300 ft (100 m) in western Maryland, and thins to zero toward the north, west, and south. This pinch-out is due to pre- and/or post-Oriskany unconformities which become more pronounced along the edges of the basin and locally in northwestern Pennsylvania and western New York.

Most of the major Oriskany fields are stratigraphic traps associated with the Oriskany pinch-out. In these fields, porosity is usually intergranular and was probably developed soon after deposition on pre-Middle Devonian topographic highs. Entrapment is due to updip loss of permeability at the pinch-out or to structural highs near the pinch-out.

Oriskany fields that are not associated with the pinch-out are structural traps characterized by fracture porosity and entrapment along anticlinal highs or against faults. Fields of this type are more common in the high plateau province and in the Eastern Overthrust belt.

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