Prior to the founding of Harrisonburg, the area was known as "Rocktown," by the settlers passing through along the Wilderness Road, a migration route originally called the "Great Warrior Path" by the Native Americans who traveled it. It seems that the name was in use throughout the 1700's and up until at least 1818, and then it seems to have been lost for a while. There's been a fairly recent resurgence of the use of "Rocktown" in Harrisonburg; it's now the name of a weekly paper in the city, a music venue, a yard shop, a gift shop, a radical info shop, and now a Property Management Company!
The area was called Rocktown because of the massive amounts of limestone that forms the basis of much of the city and surrounding area. The county around the independent city of Harrisonburg is Rockingham County, which was named after the Marquis de Rockingham, an English statesman friendly to the area. But the founding of Rockingham Co. occurred long after people started calling Harrisonburg "Rocktown."