Sideling Hill Road Cut (Washington County Maryland)

The Sideling Hill Cut located on Interstate 68 in extreme western Washington County Maryland in simple terms is a man made gap through a huge mountain. This cut eliminated the need to travel the old U.S. 40 highway which included a steep upgrade, a white knuckle hair pin turn at the top, followed by a steep descent. I can recall my first time traveling this way as a teenager having to use the old road. It was scary to say the least. Then I remember my 2nd trip - after construction on the cut was complete - and how amazed we all were. It is truly an engineering marvel.

The welcome center was opened in the early 90's. Then closed seasonally from about 2009 - 2015 until it was again opened on a year round basis. It makes for quite an interesting and photogenic stop on your trip to far western Maryland and beyond. The rock material blasted out was used to construct the highway approaching both sides of the cut to lessen the grade (which does exceed 6% still and has runaway truck ramps both east and west bound!). The bore holes (from explosive placement during construction) are still visible on both rock faces. Over the short geological time span it has been in existence - there is evidence of some erosion of the softer rock layers displayed in the cut. Winter time provides an amazing ice display on the north facing façade (eastbound lanes) as water flow through the layers of rock exits and forms a freezing cascade of ice all over the rocks. Often the ice is colored depending on the mineral content of the water. Construction of this gap interrupted the natural hydrology and water flow and did have some impacts on ridge top trees.

The gap is 340 feet deep and exposes numerous easily visible strata underlying a tough erosion resistant sandstone (Mississipian age) and conglomerate. The underlying layers are much softer and easily eroded shales and siltstones. Most of the trees along the ridge are deciduous oak and hickory, however, some evergreen (mostly pine) does exist. The mountain stretches on into Pennsylvania and in Maryland marks the eastern most ridge of the ridge and valley geological province (which includes the Hagerstown Valley) - with the Allegany Plateau to the west and the Blue Ridge to the east.

The most notable geological feature is the presence of a "synclinal ridge". If you look at the pictures the rock layers are downfolded. The rocks at the top used to be the valley bottom with ridges on each side. However, the more easily erodible formations (over time) weathered away to leave the tougher sandstone and conglomerate behind to eventually form the ridge. The ridge immediately to the west of this location (Town Hill) shares a similar geology. There are some fossils present in the rock layers (mostly plants), however some marine fossils (bivalves mostly) can be seen in some layers. The area was once at or near sea level for this to occur! This "synclinal ridge" was formed due to folding of rocks after compression from the collision of Africa and North America about 240 million years ago. Hope you enjoyed this post. It really takes me back to my days as a geography nerd when I was in school!