Coral-stromatoporoid patch reefs are present in the lower part of the McKenzie Formation of the western West Virginia subsurface. Between these organic buildups is a bedded, argillaceous dolomite with very sparse fauna, and underlying the McKenzie is the Keefer Sandstone which served as the firm substrate on which McKenzie benthic communities became established.

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During a transgression of the McKenzie sea, areas of thicker Keefer sand stood as submerged topographic highs. The local relief provided optimum sites for the patch reefs to develop and offered better protection to the fauna from being overwhelmed by incoming terrestrial clays. Conversely, the shaly interreef deposits of the McKenzie are present in areas of thinner Keefer Sandstone; they were laid down in turbid, relatively deep water between highs. A minor regression followed as represented by middle McKenzie intertidal sediments, and growth of the patch reefs ceased when the area emerged above the level of low tide.

Two southwest-northeast tracts of thicker McKenzie Formation and Keefer Sandstone mark the trends of Keefer topographic highs and associated McKenzie patch reefs. These trends now offer the best potential gas in the Middle Silurian of western West Virginia.

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