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Before logging this Earthcache as found, please send via email answers to the following questions:
Questions
- At the observation area at the top of the stairs, you can see the rock layers. Are the layers horizontal, slanted, or curved?
- Are the faces of the layers smooth or jagged? What do you think is the reason for this?
- What is the number of the PRR engine on display at the observation point?
The Allegheny Front is a portion of the escarpment that delineates the eastern edge of the Appalachian Plateau (locally, the Allegheny Plateau) and the higher ranges of the Allegheny Mountains, separating them from the lower Alleghenies to the east. At the Horseshoe Curve, the mountain face was cut away, revealing some geologic history.
Visit the Curve, find the answers to the questions below, and send the answers to the cache owner to log your find.
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The Allegheny Front
The Allegheny Front is a part of the Ridge and Valley Appalachians and is conterminous with the Eastern Continental Divide in this region.
Historically, the front was the edge of a salt evaporite basin formed at the end of the Silurian period, which created significant differences in the erosionary properties of rocks to either side of the front. The terrain differences to either side are also partially caused by the Alleghenian orogeny, in which Gondwana (modern Africa) impacted and overrode part of what is now the North American crustal plate, thrusting and piling up the ridge mountains of the physiographic regions to the east.
At the Horseshoe Curve, you can see the finest display of Late Paleozoic rocks to be found along the Allegheny Front; the rock section extends for more than 45,000 feet and exposes some 7,000 feet of rock thickness. Mostly shales and sandstones are exposed; they range in geologic age from the base of the Upper Devonian Lock Haven Formation (which underlies the Catskill Formation) to the base of the Pennsylvanian Conemaugh Group.
Layers you might see:
The Upper Devonian Lock Haven Formation contains olive-gray to olive-brown, fossiliferous shale, siltstone, sandstone, and local thin conglomerate.
The Devonian Catskill Formation, or the Catskill clastic wedge, is a unit of mostly terrestrial sedimentary rock found in Pennsylvania and New York. Minor marine layers exist in this thick, up to 10,000 feet, rock unit. It is equivalent to the Hampshire Formation of Maryland, West Virginia, and Virginia.
The Catskill is the largest bedrock unit of the Upper Devonian in Northeast Pennsylvania and the Catskill region of New York The rocks of the Catskill are predominently red sandstone indicating a large scale terrestial deposition during the Acadian orogeny. Many beds are cyclical in nature, preserving a dynamic environment during its approximately 20 million years of deposition. />
Rock outcrops (Irish Valley Member of Catskill Formation) (not at the observation point)
The Pennsylvanian system contains sandstone, conglomerate, shale, fireclay, slate, and coal.
Definitions:
The Silurian is a geologic period and system that extends from the end of the Ordovician period, about 443.7 ± 1.5 Ma (million years ago), to the beginning of the Devonian period, about 416.0 ± 2.8 Ma.
The Devonian is a geologic period and system of the Paleozoic era spanning from 416 to 359.2 million years ago.
Escarpment is "a transition zone between different physiogeographic provinces that involves a sharp, steep elevation differential, characterized by a cliff or steep slope. "
Orogeny is "mountain building".
Terrestial sedimentary rock is rock formed from sediment that accumulated above sea level.
The Horseshoe Curve
The Horseshoe Curve was constructed by the Pennsylvania Railroad (PRR) due to the difficulty of constructing a railroad through the summit of the Allegheny Mountains. It was designed by J. Edgar Thomson and Herman Haupt, opening on February 15, 1854, as part of the Pennsylvania Railroad's main line to the west.
The rail approach to the curve is on a grade of 1.75%, and the grade on the curve itself is 1.45%, to allow for the extra effort of going around the curve.
The curve has been in continuous operation since 1854. Originally comprising two tracks, it was widened to four tracks between 1898 and 1900. Conrail removed one of the tracks in 1981 and the Curve remains in this three-track configuration.
The curve's importance to railroad traffic in the U.S. was such that it was guarded by Union soldiers during the American Civil War and the Nazis attempted to sabotage it in Operation Pastorius during World War II.
Horseshoe Curve Site History
- 1879 - The park is beautified for public use.
- 1932 - A macadam road opens to the park.
- 1940 - Construction of a guest house begins (which later became a gift shop).
- 1957 - A retired steam PRR locomotive #1361 is put on display in the park. PRR transfers park operations to the City of Altoona .
- 1966 - National Historic Landmark status is granted.
- 1989 - A cooperative agreement is signed with the National Park Service to develop the site.
- 1990-1991 - Museum manages construction of a new $5.8 million facility.
- 1992 - Grand opening of the new Horseshoe Curve National Historic Landmark on April 25th.
The Curve is now a part of the National Register of Historic Places.
References:
- "Outstanding Scenic Geological Features of Pennsylvania", by Alan R. Geyer, 1979
- Wikipedia.org, "Horseshow Curve (Altoona, Pennsylvania)"
- "Horseshoe Curve Remembered", by Frederick A. Kramer
- http://www.absoluteastronomy.com/topics/Horseshoe_Curve_%28Pennsylvania%29
Before logging this Earthcache as found, please send via email answers to the following questions:
Questions
- At the observation area at the top of the stairs, you can see the rock layers. Are the layers horizontal, slanted, or curved?
- Are the faces of the layers smooth or jagged? What do you think is the reason for this?
- What is the number of the PRR engine on display at the observation point?