Alternatively, the area could be limited to the drainage of the Shenandoah River, excluding Rockbridge County. The watershed divide between the Shenandoah and James rivers is close to the Augusta/Rockbridge county line. Just south of Staunton, the Steeles Tavern exit on Interstate 81 identifies the high point between the Potomac and James river watersheds.
The limestone soils enabled Augusta and Rockingham to become the dominant agricultural producers in Virginia, and the famous McCormick reaper was developed on a farm near Steeles Tavern. (If you visit the historical site, see if you can identify if the stream flowing from the farm is headed to the Potomac or the James...) Because there is no obvious physical difference in the landscape or barrier to travel on the southern end of the valley until you reach the James River, there is no obvious cultural difference between residents of Augusta and Rockbridge counties. Wheat farming was common throughout the valley, south to Lexington and north to Winchester.
Up the Valley: The Shenandoah River runs north. The mouth of the river is at Harpers Ferry, where the Shenandoah joins the Potomac. If you go upstream, you are going south. If you hear someone refer to a place "up the valley," they mean south towards Staunton and the divide at Steele's Tavern on the Augusta/Rockbridge County border. You may be accustomed to seeing maps hung vertically on the classroom wall, with north at the top. Don't make the mistake of assuming that "uphill" means going north. The Upper Valley Regional Park Authority is based in Grottoes, not Harpers Ferry...