The Great Valley is that portion between Fort Lewis Mountain and the Blue Ridge. Interstate 81 runs through the Valley but not at all along its floor; rather it hugs the ridge at an elevation of about 350 feet above the City of Roanoke in the Valley floor. Finally the higher Cumberland Plateau is reached, up to about 3000 feet in elevation.
Virginia is unusual among Eastern states in having such diversity of topographic regions. For example, Abingdon in Washington County is located in the Ridge and Valley region 25 miles from the Appalachian Plateau and the Blue Ridge, and less than 100 miles from the Piedmont. Similarly, Northern Virginia straddles the Coastal Plain, Piedmont and Triassic Lowland and is less than 25 miles from the Blue Ridge and Great Valley. Such diversity within small areas is uncommon in most regions of the country.
In broad outline the topography of Virginia east of the Blue Ridge is simple; the flat Coastal Plain and the rolling Piedmont "tilt" to the southeast. This is evident from the pattern of all the major rivers: the Potomac, Rappahannock, York, James, Nottoway, Meherrin, Roanoke and Dan. West of the Blue Ridge the pattern is much more complex because, starting in the north, the Valley first "tilts" northward as evidenced by the northeast-flowing Shenandoah.
Then a divide near the Augusta-Rockbridge county line separates the headwaters of the Shenandoah from the south-flowing tributaries of the James (the Jackson, Maury, and Cowpasture Rivers). Farther south, the New River flows northwestward into West Virginia and the Ohio River. Finally, in Southwest Virginia the Valley slopes south again as indicated by the various forks of the Holston which flow southwestward to the Tennessee River.
Three of these drainage areas are shown on the elevation profile. The first is indicated by Sandy Ridge near the junction of the boundaries of Dickenson, Wise and Russell counties. It is marked on the elevation profile as the Tennessee Valley Divide because it separates that river's drainage from drainage of the Ohio River. Ohio River system drainage does not show on the elevation profile at this point, however, because those rivers flow north from Sandy Ridge and are not intersected by the profile. On the profile, rivers to the west of Sandy Ridge drain into the Powell; rivers to the east drain into the Clinch; both then feed into the Tennessee. Rich Mountain in Tazewell County is the next major divide. It separates tributaries of the Clinch from those of the New River. Rich Mountain is also the highest point along the elevation profile, approximately 3540 feet.
Less than half a mile south of the line of the profile, Rich Mountain reaches its highest elevation at 4270 feet. Tributaries of the New River lie to the east of Rich Mountain until the New River itself is reached at the Pulaski-Montgomery County boundary. At Blacksburg near the small Virginia Tech Airport, lies the divide between tributaries of the New River and tributaries of the Roanoke River. The next divide is near the Bedford County-Lynchburg City line which separates tributaries of the Roanoke River from those of the James. Most remaining rivers are part of the James drainage system until east of Richmond, the Pamunkey, Mattaponi and Rappahannock are crossed. Then Eastern Shore drainage is reached where small rivers flow either into the Chesapeake or the Atlantic.
As students draw their own elevation profiles, an important consideration is to select a route with diversity in elevation. Any profile that crosses only the Coastal Plain and Piedmont will be relatively uninteresting. Some students may wish to construct a profile along a road. For example a profile could be made of Route 58 across the southern edge of the state, or Route 60 from Covington to Hampton Roads. If this is done the student should remember that the profile no longer reflects a straight line although it may be portrayed as such.
If a student chooses a road to profile it is best to avoid interstate highways because so much of the landscape along these routes has been artificially added or removed to make the road as level as possible. Similarly a profile along the course of a river will show less dramatic changes in elevation because of the natural downcutting and infilling of water action. A profile of the Appalachian Trial would show little change in topography because so much of it is at high elevation.
One handy source of information that may be of help to students in selecting a profile is the Department of Transportation's road map of Virginia which gives elevations of major peaks and passes where roads cut across the Blue Ridge. A second source, the Virginia Statistical Abstract, published by the Center for Public Service at the University of Virginia, gives the elevations of the fifty highest mountains in Virginia.
Go to the second part on Constructing the Profile