The Folded Rocks of Sideling Hill Road Cut

The Sideling Hill is a long, steep, narrow mountain ridge that runs north to south across western Maryland in Washington County, in the United States. For many centuries, this mountain had blocked the path of many travellers who wished to go from Maryland to northeast West Virginia and vice versa. Travellers had to decide whether they wanted to go around it or over it, but both routes being treacherous, resulted in many mishaps. The first tunnel was blasted through the rocks of Sideling Hill in 1873–74 for the East Broad Top Railroad. This was followed by at least a couple more. The original railroad tunnel ceased operation in 1956, and the one opened in 1940 is now abandoned. A few decades later, when the Maryland State Highway Administration was laying down Interstate 68 across the state of Maryland, they decided that another tunnel through Sideling Hill would be too expensive. Instead, they decided to cut a deep notch across the hill and lay the road through it. After excavating 10 million tons of rock, engineers discovered they had exposed an unusual geologic structure — a syncline of tightly folded rock strata dating back more than 350 million years. Sunrise hits the south side rocks of the Sideling Hill road cut along I-68. Photo credit A syncline is a fold in which the strata on either side dip inward toward the axis. Such folding resulted from the enormous compressional stresses developed in the Earth's crust by the collision of the North American and African continents. The 100-meter-deep cut, located on Interstate 68, about 11 km (7 miles) west of Hancock, is considered one of the best rock exposures in the United States. It provides an excellent outdoor classroom where students of geology can observe and examine various sedimentary rock types, structural features, and geomorphic relationships. A walkway over the highway and steps leading to the rock formations allow students and visitors alike to take a closer look.