Blue Ridge and Shenandoah Valley
The collisions of continents, and the erosion by wind and rivers, have left impacts obvious to even the untrained eye. In 1670, the early explorer John Lederer understood that Virginia was not a homogenous place. Centuries before aerial photography and satellite imagery, Lederer recognized that every part of the colony did not look just the same. He classified the landscape by topography:1
Lederer probably looked west from the Blue Ridge, and may have gone down into the Shenandoah Valley after climbing through different passes or low "gaps" in the ridge. Had he explored further west, he may have recognized the distinctive character of the valleys and ridges west of the Blue Ridge deserved their own label, as did the flat highland even further west that we now call ther Appalachian Plateau.
Not everyone draws the exact same physiographic boundaries for locations in Virginia area. Typically, geologic boundaries distinguised by separate types of rock that an be mapped) are defined more precisely than physiographic region boundaries.
The boundaries of geologic provinces based on bedrock do not match up exactly with the edges of physiographic provinces. The geologic and physiographic maps on William and Mary's Geology of Virginia site show the primary difference: the "Foothills subprovince" east of the steep slopes of the Blue Ridge mountains.
The bedrock that defines the eastern edge of the Blue Ridge geologic province (Catoctin greenstone) extends east, beyond Charlottesville. However, erosion has flattened the eastern edge of that geologic formation, so the Charlottesville website says the city is "[s]ituated within the upper Piedmont Plateau, at the foothills of the Blue Ridge Mountains and at the headwaters of the Rivanna River..."2 and the most active land conservation group in the Blue Ridge province calls itself the Piedmont Environmental Council.
The standard list of physiographic provinces for Virginia includes:
This list omits the area east of the Coastal Plain, under the water of the Atlantic Ocean since the ice sheets started melting faster than they were growing 18,000 years ago. The now-submerged part of the Coastal Plain, the Continental Shelf, can be treated as an additional physiographic province. The Continental Shelf extends from the shoreline into the Atlantic Ocean, eastward to a depth of about 200 meters. There, edge of the continent drops down relatively steeply to the deep bottom of the Atlantic Ocean.
If you want to be very specific about the underwater physiographic provinces, then you can separate the flat continental shelf from deep ocean bottom, and define a Continental Slope zone with a Continental Rise near the very bottom, where sediments washing off the slope have accumulated.
The Continental Slope is a steep underwater hillside, droping down from the Continental Shelf to the deep ocean bottom known as the Abyssal Plain. From the beaches of Virginia out to the slope, the bedrock is still continental crust - with a coating of ocean sediments and a column of water on top. The Continental Slope marks the edge of the continental tectonic plate. East of the Continental Slope, bedrock is heavy, iron-rich basalt. The oceanic crust extends further eastward to the Mid-Atlantic Ridge, the range of underwater mountains in the middle of the Atlantic Ocean where basaltic magma oozes up regularly via a crack in the crust.
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John Lederer was one of the first Europeans to leave a record of his transect across the physiographic provinces of eastern Virginia. There may have been earlier European explorers, and certainly there were earlier Native Americans - but they left no written reports to document their discoveries. Some European may have beaten John Lederer to the western edge of the colony, but Lederer gets the credit.
There's a monument to him on Route 55 at Markham, east of Front Royal. It is located on his supposed route through Manassas Gap; there's a fair chance that he once stood at that very spot. The monument is one of the many pieces of visual clutter that, if you slow down and look carefully out the window, can make traffic headaches a little less burdensome. From the top of the Blue Ridge, Lederer saw the Shenandoah Valley and North Mountain on the western side. Even if the day was clear, however, he probably did not see the Allegheny Front in what is known today as West Virginia. The "front" is the edge of the Appalachian Plateau, on the west side of the Valley and Ridge province. On the Appalachian Plateau, the layers of rock are no longer folded extensively, in contrast to the extensive deformation of rock in the Valley and Ridge province The impact of Africa and North America folded and faulted the rock layers across Virginia, compressing and tilting them until the energy of the collision was dissipated. The boundary, where those rock layers were not reshaped by the collision, is the western edge of the Valley and Ridge physiographic province and the eastern edge of the Apppalachian Plateau. West of the Shenandoah Valley, the Valley and Ridge province extends into West Virginia. In Virginia, the Allegheny Front is most visible in the southwestern part of the state. |
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Lederer would have seen Massanutten Mountain clearly, between his location on the Blue Ridge and the horizon. Massanutten may be a "mountain," but from both a geologic and physiographic perspective, that mountain is just one of the many ridges in the Valley and Ridge province. The volcanic bedrock of the Blue Ridge (the location of Shenandoah National Park and the Blue Ridge Parkway) is dramatically different from the younger sedimentary bedrock of Massanutten Mountain to the west.
If you stand on Skyline Drive and look west from Swift Run Gap (where US 33 crosses the mountain), you'll see that south of Route 33 and Massanutten Mountain, there's just one wide Shenandoah Valley stretching between the Blue Ridge and West Virginia. The valley (known by different names, and sometimes just called the Great Valley) extends south down to Staunton, Lexington, Roanoke, and on to the Tennessee border and north through Pennsylvania to New York.
North of Route 33, Massanutten Mountain splits the Shenandoah Valley. Between the Blue Ridge and Massanutten, from Waynesboro in the south to Front Royal in the north, the eastern part of the Shenandoah Valley is also called the Page Valley. If you visit Luray Caverns, you are in the Page Valley. You can drive along Route 340, or float on the South Fork of the Shenandoah River, throughout the Page Valley subunit of the Shenandoah Valley.
West of Massanutten, Interstate 81 and the North Fork of the Shenandoah River run through the wider part of the Shenandoah Valley.
If you want to be a physiographic province "lumper" rather than a "splitter," you could combine all the western Virginia ridges (including the Blue Ridge) into one or two provinces. That approach would eliminate the Blue Ridge as a unique province. Lumpers treat the Blue Ridge as just one of the many ridges in an expanded interpretation of the Valley and Ridge province. Cultural geographers may even lump the Blue Ridge together with the Appalachian Plateau and refer to the "Appalachians" in various discussions of colonial history and frontier settlement.
Lumping can generate substantial confusion, especially regarding the definition of "Appalachia." Physical geographers and cultural geographers do not always draw lines in the same places; "mountain culture" may refer to multuiple physiographic provionces. The characters in the 1960's hit TV show The Beverly Hillbillies were theoretically from the Ozarks of Missouri/Arkansas, not the Appalachians. The characters in The Waltons reflected a very different mountain culture, from the Blue Ridge Mountains southwest of Charlottesville.
If you are a splitter, you can separate not only the Blue Ridge from the Valley and Ridge, but also the "Great Valley" or Shenandoah Valley into a sub-unit of the Valley and Ridge physiographic province:
The edges of physiographic regions are not based on cultural or biological features, such as political/urban boundaries or forested/developed lands. So - why would anyone bother to define areas with consistent landforms?
The Virginia Natural Heritage Program identifies areas of special significance within separate sections of the state. Physiographic provinces are particularly useful for identifying natural communities and where rare/endangered species should be protected. Type in "physiographic region" or "physiographic province" in a search engine and note how many studies of birds, plants, and preservation of natural areas organize information and make recommendations based on physiographic province boundaries.
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The names of physiographic regions may not match up exactly - but in many cases, the boundaries are consistent with other classification systems. The "Cumberland Plateau" of the Virginia Natural Heritage Program is equivalent to the "Appalachian Plateau" defined by others. Also, you'll see different spellings in different places. If you want to know if Allegheny or Alleghany is the correct spelling, ask a local resident... and go with their advice.
Note that the edges of physiographic provinces are not mapped at a detailed scale, such as the 1:24,000 quadrangle maps used by hikers or the 1:400 scale plats used by county assessors for property tax purposes. Physiographic provinces define regional boundaries intended for general orientation, so specific sites (such as those being examined in environmental impact statements) can be put into context. Locations of property boundaries, roads, archeological sites, and wetlands are mapped far with far more detail that the edges of the physiographic regions. For example, one study at the Virginia Institute of Marine Sciences drew a map showing the physiographic provinces based on county boundaries. Obviously the straight lines defined by county surveyors do not have a direct relationship with Virginia's natural features, but organizing information by county and physiographic province can still be useful.
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 simplified physiographic boundaries Source: "A Review of Nontidal Wetland Projects and Impacts in Virginia, 1991 - 1993 |
The boundaries of the current physiographic provinces are not permanent. During the last Ice Age, sea levels were 350-400 feet lower3 and much of today's Outer Continental Shelf was exposed. Some of Virginia's earliest archeological sites are probably buried under salt water and sediments deposited in the last 10,000 years as the sea levels have risen.
During warmer epochs when glaciers melted and sea level rose even higher, the edge of the Atlantic Ocean would have been roughly where I-95 is located today. Go back further in geologic time, such as 200 million years ago when Pangaea was splitting up, and the physiographic provinces of Virginia would have been dramatically different.
