Sideling Hill, also Side Long Hill, is a long, steep, narrow mountain ridge in the Ridge-and-Valley (or Allegheny Mountains) physiographic province of the Appalachian Mountains, located in Washington County in western Maryland and adjacent West Virginia and Pennsylvania, USA. The highest point on the ridge is Fisher Point, at in Fulton County, Pennsylvania. Geology Sideling Hill is a syncline mountain, in a region of downward-folded (synclinal) rock strata between two upfolded anticlines. The ridge is capped by an erosion-resistant conglomerate and sandstone of Mississippian (early Carboniferous) geologic age, the Purslane Sandstone of the Pocono Formation. The ridge's slopes are formed of much more easily eroded kinds of rock, including the Devonian-Mississippian Rockwell Formation, with long, narrow valleys paralleling the ridge on either side. Ecology Most of the crest of Sideling Hill is forested, primarily with various deciduous tree species such as oaks (Quercus) and hickories (Carya), along with occasional evergreen pines (Pinus). Highway, railroad, and canal crossings Only a few major highways, one active and two former railroads, and one former canal cross this steep mountain ridge. East Broad Top Railroad Tunnel (Pennsylvania) The East Broad Top Railroad constructed a tunnel through Sideling Hill in 1873–1874 as part of its mainline construction. The tunnel predates the South Pennsylvania Railroad tunnel construction to the south by eight years. The tunnel is single-tracked, and curved at each end. It originally had a stone portal on its eastern (RR North) end and a natural stone portal at its western (RR South) end, but about 1919 the north portal was replaced with a concrete one. The north portal was equipped with doors to prevent wind from blowing through the tunnel as the wind caused water percolating into the tunnel to freeze on the tracks in the winter. In 1911, this ice caused the brand new locomotive #12 to derail its pilot axle inside the tunnel then derail the entire locomotive at the Kimmel switch just beyond the tunnel. In the 1940s, the doors were equipped with remote actuators mounted on poles a few hundred feet before each portal. This allowed the crews to open and close the doors without stopping. The system did not work flawlessly and a door was ripped off by a caboose cupola. The tunnel was in service from 1874 until the railroad ceased operations in 1956. The line is technically out of service (but not abandoned), and the track is