Interstate 68 road cut in Sideling Hill in western Maryland
|Elevation||2,310 ft (704 m)|
|Location||West Virginia, Maryland, and Pennsylvania, U.S.|
|Range||Ridge-and-Valley province, Appalachian Mountains|
|Topo map||USGS Wells Tannery|
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. Following the sequence of points found in the USGS search query , the highest point on the ridge is Fisher Point, at 2,310 feet (700 m), in Fulton County, Pennsylvania.
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.
|This section requires expansion. (November 2011)|
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 1873–74 as part of its mainline construction. The tunnel predates the South Pennsylvania Railroad tunnel construction 11 miles (18 km) 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 still in place through the tunnel, although not serviceable. The tunnel and rail line are private property and not open to the public.
Pennsylvania Turnpike (I-76) 
The Pennsylvania Turnpike (Interstate 76) crosses Sideling Hill east of Breezewood, Pennsylvania, bypassing the two-lane Sideling Hill tunnel and the nearby Rays Hill tunnel that were formerly used by the Turnpike. Completed at a cost of $17,203,000, the Sideling Hill bypass opened on November 26, 1968.
Sideling Hill Tunnel (Pennsylvania) 
The Sideling Hill Tunnel, through Sideling Hill in Pennsylvania east of Breezewood, is currently in its third phase of life. In the 1880s, a tunnel was partially bored through the mountain by the South Pennsylvania Railroad. The railroad project ceased, and the tunnel was left abandoned. When construction of the Pennsylvania Turnpike was begun in the 1930s by the Pennsylvania Turnpike Commission on the right-of-way of the old South Pennsylvania Railroad, the tunnel was completed for highway use by the Turnpike.
The tunnel, at 6,782 feet (2,067 m) long the longest of the seven original Turnpike tunnels, was used from the Turnpike's opening in 1940 until 1968. Due to increasing traffic on the highway, the turnpike commission began upgrading all of its two-lane tunnels, constructing twin bores for its tunnels through the Allegheny, Tuscarora, Kittatinny, and Blue mountains, and bypassing the tunnels under Laurel Hill, Rays Hill, and Sideling Hill with new, four-lane highways climbing the adjacent hills. The Sideling Hill tunnel and the nearby Rays Hill tunnel, along with connecting segments of four-lane highway, were used for many years as a testing facility for new highway technologies.
In 2001, the Sideling Hill Tunnel was sold to the Southern Alleghenies Conservancy for $1, which now operates it as a bike trail.
Sideling Hill Road Cut (I-68 and U.S. 40, Maryland) 
The Sideling Hill Road Cut on Interstate 68 and U.S. 40 is a 340-foot (100 m) deep notch excavated from the ridge of Sideling Hill, about 7 miles (11 km) west of Hancock in Washington County, Maryland. It is notable as an impressive man-made mountain pass, visible from miles away, and is considered to be one of the best rock exposures in Maryland and the entire northeastern United States. Almost 810 feet (250 m) of strata in a tightly folded syncline are exposed in this road cut. Although other exposures may surpass Sideling Hill in either thickness of exposed strata or in quality of geologic structure, few can equal its combination of both. The exposed rocks consist of the Devonian-Mississippian Rockwell Formation, underlying the Mississippian Purslane Sandstone.
Rest stop and former Exhibit Center 
A highway rest stop, located near the eastern side of the Sideling Hill Road Cut on Interstate 68 west of Hancock, includes a pedestrian bridge crossing I-68, connecting the eastbound and westbound rest areas and offering views of the cut, in which stopping is prohibited.
The rest stop formerly included the Sideling Hill Exhibit Center, a four-level geological museum and travel information center which opened in 1991. Due to state budget cuts, this facility was closed on Aug. 15, 2009, as part of a $280 million budget reduction package, saving the state about $110,000 annually. Before its closing, the center served about 95,000 visitors a year, at a cost of about $1.16 per visitor.
Sideling Hill exhibit transferred to Hancock Museum and Visitor's Center, Hancock Maryland.
Exhibits in Hancock, Maryland 
National Road (Scenic U.S. 40) 
Potomac River Water Gap 
The water gap cut through Sideling Hill by the Potomac River southwest (upstream) of Hancock, Maryland, provides a low-level crossing of the ridge for the CSX Railroad, formerly the main line of the Baltimore and Ohio (B&O) Railroad, on the southern (West Virginia) side of the river, and on the northern (Maryland) side, the former Chesapeake and Ohio Canal, now a national historical park, and the former Western Maryland Railroad (now a rail trail).
See also 
- Maryland Geological Survey, "Geology of the Sideling Hill Road Cut", accessed 2009-03-09.
- Sideling Hill Exhibit Center to close (The Herald-Mail, July 22,2009)