| Allegheny Front | |
|---|---|
 Dans Mountain, part of the Allegheny Front in Maryland | |
| Highest point | |
| Peak | Mount Porte Crayon, Randolph/Pendleton Co. border,West Virginia |
| Elevation | 4,774 ft (1,455 m) |
| Coordinates | 38°55′44″N79°27′22″W / 38.92889°N 79.45611°W /38.92889; -79.45611 |
| Geography | |
 The Allegheny Front (not specifically marked on the map) forms the western boundary of the indicated "Ridge & Valley" region of the Appalachians. | |
| Country | United States |
| States |
|
| Range coordinates | 39°04′23″N79°17′53″W / 39.07306°N 79.29806°W /39.07306; -79.29806 |
| Parent range | Allegheny Mountains of theRidge-and-Valley Appalachians |
| Geology | |
| Orogeny | Alleghenian orogeny |
TheAllegheny Front is the major southeast- or east-facingescarpment in theAllegheny Mountains in southernPennsylvania, westernMaryland, easternWest Virginia, and westernVirginia. The Allegheny Front forms the boundary between theRidge-and-Valley Appalachians to its east and theAppalachian Plateau (locally called theAllegheny Plateau) to its west. The Front is closely associated with theAppalachian Mountains'Eastern Continental Divide, which in this area divides the waters of theOhio/Mississippi river system, flowing to theGulf of Mexico, from rivers flowing intoChesapeake Bay and from there into theAtlantic Ocean.
The Allegheny Front and the Eastern Continental Divide do not always coincide; for example, theNorth Branch of the Potomac River begins well west of the Front, at theFairfax Stone near the southwestern tip of Maryland, about 10 miles (16 km) and across the actual divide from the headwaters of theYoughiogheny Riverdraining northwards into theMonongahela and Ohio rivers. The Front and the Divide diverge completely in central Pennsylvania where theWest Branch Susquehanna River originates north of the Allegheny Front.
The Allegheny Front is one of the windiest spots east of theMississippi, leading to the recent establishment ofwind farming there.[citation needed]
The Allegheny Front forms part of theAppalachian Structural Front, separating theAppalachian Plateau from the Appalachians'Ridge and Valley Province.[1] The various otherescarpments along this structural feature include theCatskill Escarpment to the northeast and theCumberland Escarpment to the southwest.[1] The Allegheny Front extends for about 180 miles (290 km) southwesterly from south-centralPennsylvania throughwestern Maryland, then divides theeastern panhandle of West Virginia from the rest of that state.
The name "Allegheny Front" is applied to the escarpment throughout much of its extent, although it is little used in Maryland.
The highest part of the crest of the Allegheny Front is also its southernmost high point,Mount Porte Crayon at 4,770 feet (1,450 m), on thePendleton/Randolph county line in West Virginia. Its lowest point, 790 feet (240 m), is along theNorth Branch of the Potomac River nearKeyser, West Virginia.[2] Other high points along the front include theDolly Sods Wilderness in West Virginia, a broad, rocky plateau at an elevation of about 4,000 feet (1,200 m); Dan's Rock onDans Mountain in Maryland at 2,895 feet (882 m); andBlue Knob in northernBedford County, Pennsylvania, with an elevation greater than 3,120 feet (950 m).
Local segments of theEastern Continental Divide usually pass within a few miles of the Allegheny Front and in many places coincide with it; this divide between waters of theAtlantic Ocean and theGulf of Mexico separates the westward-flowingOhio River watershed from the eastward-flowing watersheds of theSusquehanna,Potomac, andJames rivers. Numerous eastward-flowing streams have their headwaters incised into Allegheny Front, displacing the divide westward from the front, including the North Branch of the Potomac River west ofCumberland, Maryland, which originates well into theAppalachian Plateau at the Fairfax Stone, just south of Maryland's southwestern tip. No waterway crosses the front from east to west.
The Allegheny Front begins in central Pennsylvania northwest ofLock Haven and extends southwest parallelingBald Eagle Mountain andBrush Mountain to its east. The front continues to a point north of the Pennsylvania/Maryland boundary where it is offset about 10 miles (16 km) to the east as it changes from the bold escarpment that characterized it west ofAltoona to its more gentle rise in Maryland.
Across theMason–Dixon line in Maryland, the front becomesDans Mountain, west ofCumberland, which reaches 2,895 feet (882 m) at Dan's Rock. Along Maryland's southern border, the North Branch of the Potomac River cuts down through the front at 790 feet (240 m) just west ofKeyser, West Virginia.
South of the Potomac in West Virginia, the front continues through theMount Storm area, then passes along the eastern edge of Dolly Sods, a wide plateau ofPottsville conglomerate bedrock at about 4,000 feet (1,200 m) elevation. From the Sods, the front continues southward as an increasingly steep escarpment west of the North Fork of theSouth Branch Potomac River, with theRoaring Plains West Wilderness continuing the high plateaus of the Dolly Sods area along the escarpment's crest. The Allegheny Front's southern end isMount Porte Crayon (4,770 ft or 1,450 m), after which the land drops steeply toSeneca Creek, west ofSeneca Rocks.[4]
South of Mount Porte Crayon and Seneca Creek, the Appalachian structural front is less clearly unified. Pottsville-cappedSpruce Mountain, south and east of Seneca Creek, continues the Allegheny Front's geology southward;[5] this ridge reaches an elevation of 4,863 feet (1,482 m) atSpruce Knob, West Virginia's highest point. Similarly steep escarpments sharing much of the same geologic structure are also present nearby along the eastern slopes ofAllegheny Mountain andBack Allegheny Mountain (along with the southern end ofShavers Mountain), but these mountains lack the Pottsville caps characteristic of the Allegheny Front.[5] Allegheny Mountain's long, nearly level crest is generally about 4,000 to 4,200 feet (1,200 to 1,300 m) in elevation, with Paddy Knob reaching 4,477 feet (1,365 m). High points on Back Allegheny Mountain and adjacent Shavers Mountain includeGaudineer Knob (4,432 ft or 1,351 m) andBald Knob (4,842 ft or 1,476 m); these two mountains form a part of the divide between theMonongahela River andNew River portions of the Ohio River watershed.
Most of the Allegheny Front is capped by a nearly horizontal, erosion-resistantstratum (rock layer) of whitePottsville conglomerate, sometimes where flat with youngerCarboniferous strata on top.[5] Thesilica-cemented,gravel-containing Pottsville rock formed as part of a vast delta in thePennsylvanian period.[6]
The region was then uplifted and folded during theAlleghenian orogeny about 320-250 million years ago, during theCarboniferous[7] andPermian periods, forming the modernAppalachian Mountains as theNorth American andAfrican tectonic plates collided.[6]
Subsequent erosion (for more than 200 million years) has preferentially removed various softer surrounding rocks, especially the easily dissolvedGreenbrier limestone, leaving areas of the hard Pottsville conglomerate as acaprock protecting softer rock strata immediately beneath. The Pottsville outcrops conspicuously in various more exposed areas along the front's eastern edge. Many of these clifftops offer broad scenic views, unlike most mountaintops within the generally forested Appalachians, and the more readily accessible are popular tourist destinations, including Dan's Rock on Dans Mountain in Maryland and the Dolly Sods and an overlook alongU.S. Route 50 in West Virginia.
Since the eastern side of the front is drained byChesapeake Bay stream that drop fairly rapidly through theRidge and Valley Province to the low-elevation waters of theGreat Appalachian Valley, erosion on the eastern slope of this caprock layer has been much more intense than on the western slope, where drainage to low elevations is spread over a greater distance (particularly considering streammeanders) through the Appalachian Plateau to the Ohio River. These contrasting patterns of erosion produce a steep escarpment along much of the front's eastern edge, with the mountains west of the front generally grading more gently into the Appalachian Plateau.
The nearly continuous high elevation and clifftop bedrock exposures of the Allegheny Front provide an important corridor of upland habitat in the central Appalachian Mountains.
During the fall, the Allegheny Front is associated with an importantflyway for migratory birds traveling from their northern breeding grounds to their southern wintering sites. In good weather, the birds can be seen from late morning, when they take advantage of thethermals (rising pockets of warm air) to facilitate flying, until the thermals cease in late afternoon.[8]
Among the bird-banding stations and migratory bird observatories associated with this flyway are:
In theDolly Sods Wilderness of West Virginia, and southward toward Mount Porte Crayon, the front is topped for more than 10 miles (16 km) by a broad, nearly flat plateau with many wide areas of exposed bedrock along the edge of the escarpment's 2,800-to-3,200-foot (850 to 980 m) drop[10] to the North Fork River to the east, along the front's base. Many of these windswept cliff-edge outcrops are sparsely vegetated, with occasional one-sided (flagged) red spruce (Picea rubens) trees, and open habitats dominated by various low-growing Appalachian andboreal plant species.[11]
The long, steep, nearly continuous, often windswept escarpment of the Allegheny Front has both positive and negative effects on society and culture in the central Appalachians region.
Few roads or railroads cross the Allegheny Front, limiting transportation and communication between the regions to its east and west. Establishing passage of the front was key to the development of the U.S. railroad network during the second half of the 19th century, thereby connecting theMidwest by rail with theAtlantic seaboard. ThePennsylvania Railroad built theHorseshoe Curve track section west ofAltoona, so that freight trains could ascend or descend to or from the Allegheny Plateau to the west.
Substantial portions of the Allegheny Front's crest and slopes are parts of a national forest (theMonongahela in West Virginia) or various state, local, or private wildlands parks or preserves. The few readily accessible scenic viewpoints atop the Allegheny Front are popular tourist destinations. TheSkyline Overlook alongU.S. Route 50 in West Virginia is readily accessible by a major road. The front is also a significant part of scenic views from various highways and mountains to its east, such asNorth Fork Mountain in West Virginia.
The NedPower Mount Storm Wind Project in West Virginia includes 132wind turbines along 12 miles (19 km) of the Allegheny Front inGrant County nearMount Storm. Constructed between 2006 and 2008, it generates up to 264 megawatts of electricity for the mid-Atlanticpower grid, enough to service about 66,000 homes and businesses.
In December 2016, Save Our Allegheny Ridges, a group that opposes energy development on forested mountaintops, said in a news release that Invenergy plans to install a series of wind turbines atop Shaffer Mountain in Somerset County just a few miles north of the Allegheny Front Hawk Watch.[12]