Karst topography is defined as topography that is a result of water dissolving various layers of underground rock over a long period of time. Most of the time it relates to the dissolving of calcium carbonate in limestone. Slightly acidic rainwater can slowly convert the carbonate into carbonic acid which is water soluble. The topography is then defined by underground rivers, sinkholes, and also underground caverns. Virginia actually has a rather large area of Karst topography. The entire western border of the state is called the Shenandoah Valley and it is defined by Karst topography. There are numerous underground rivers in this area. You will see rivers running along the surface and then disappearing underground or rivers emanating from the edge of a mountainside. There are also numerous sinkholes in the area and several notable caverns including Luray Cavens and Grand Caverns.