The Subterranean/Sink class includes natural communities that occur in karst landscapes below the general land surface. These karst features form from the underground dissolution of limestone, dolomite, or gypsum. The Subterranean/Sink class includes one ecological group, Karst. This ecological group includes two natural community types, cave and sinkhole, which are distinguished based on their distinct landscape settings. A cave is a cavity that has formed beneath the earth’s surface, and a sinkhole is a subsidence or depression in the earth’s surface caused by the dissolution of the surficial bedrock.