Geology of the New York City Region

30. Highland Mills, New York

Steeply dipping strata of Middle Devonian age within the Green Pond Outlier are well-exposed in rail bed excavations for the Hudson Valley Conrail line in Highland Mills, New York (Figure 68). To get there, follow Route 32 North into Highland Mills and turn right onto Park Avenue, and drive .3 mile to a gravel turnoff and parking area at the abandoned location of the Highland Mills train station (now only an power substation remains). Be EXTREMELY CAREFUL while examining these exposures, in that high speed train approach almost quietly without warning (their sound is masked by noise from the Thruway nearby). This rail line follows Woodbury Creek northward along the eastern flank of Schunnemunk Mountain.

Outcrops of Devonian strata along railroad line at Highland Mills, New York
Figure 68. Exposures of steeply dipping Middle Devonian sandstone and shale along the Conrail tracks in Highland Mills, New York. The eastern flank of Schunnemunk Mountain is on the left.

The Middle Devonian Esopus Formation (undifferentiated) crops out immediately across from the substation. This fine-grained sandstone with interbedded shale displays brachiopod shell hash layers preserved as iron-stained molds and shows evidence of heavy bioturbation by marine invertebrates (Figure 69). The strata is dipping steeply in a northwest direction at about a 65 tilt. The walk northward along the path besides the tracks (not on the tracks!) provides an opportunity to examine progressively younger units which are increasingly less fossiliferous and more haley (an indication of progressively deepening water conditions). About a mile northward along the tracks are exposures of the brownish-red Bellvale Sandstone. From here, the strata grows progressively coarser-grained up-section until coarse puddingstone conglomerate dominates the ridge of Schunnemunk Mountain (on the west side of the valley).

Devonian fossils, Esopus Formation, Higland Mills, New York
Figure 69. Molds of brachiopods in sandstone from the Middle Devonian Esopus Formation,
Highland Mills, New York.
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Last modified: 3/11/2019