Reefs are found in the outcrop sections of several Lower and Middle Devonian units in New York State. The most prominent of these occurs in the Edgecliff Member of the Onondaga Limestone.

The Onondaga Limestone was first described and named by James Hall of the New York Geological Survey in 1839. The present fourfold division of the Onondaga, in descending order, Seneca, Moorehouse, Nedrow, and Edgecliff, was proposed by Oliver in the early 1950s. The type section is located in Onondaga County, New York. In the subsurface, the uppermost Seneca Member is a massive limestone and can only by separated from the similar underlying Moorehouse Member by the presence of the Tioga Bentonite Bed, which gives a characteristic peak on the gamma ray log.

The Seneca is absent in the central-southern part of New York, where a pronounced thinning of the Onondaga occurs. The Moorehouse is a massive cherty limestone and is also missing in the extreme central-southern part of New York in the previously mentioned area of thinning. The Nedrow is a shaly cherty limestone and is persistent throughout the state and in the area of thinning, except over known subsurface reefs in the underlying Edgecliff.

The lowermost Onondaga member, the Edgecliff, is a coarse-grained light-gray to grayish-white biostromal limestone, present in an area from northeastern southwestward through central New York.

In eastern and southeastern New York this unit is represented by an argillaceous facies, whereas in far western New York it is highly cherty. The Edgecliff shows a pronounced thinning in central and southern New York and in north-central Pennsylvania, where it is mostly 10 ft or less thick. In the southwestern part of this thin area, three subsurface Edgecliff reefs, all 150-200 ft thick and containing gas, have been discovered since 1967. At least 21 smaller reefs are known in the outcrop section of this member in eastern New York, one in central New York and two in the Buffalo area. The reefs were formed in a clear-water shallow subtidal environment on the Edgecliff platform.

Biostromal facies and reefing are also present on the outcrop in several zones in the Middle Devonian Hamilton Formation, which overlies the Onondaga. Most important of these zones are in the Ludlowville Member of the Hamilton in the Syracuse area of central New York. Two of these zones, the Joshua and Staghorn Point, occur over areas of 40 and 120 sq mi, respectively, according to Oliver. No reef buildup in these zones has been encountered in drilling as yet, but no systematic search has been made for reefs in the subsurface.

Several smaller reefs are known from outcrops of the Coeymans Formation of the Helderberg Group in central New York and northwestern New Jersey.

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