Karst (kärst) [key], Ital. Carso, Slovenian Kras, limestone plateau, W Slovenia, N of Istria and extending c.50 mi (80 km) SE from the lower Isonzo (Soča) valley between the Bay of Trieste and the Julian Alps. It is characterized by deep gullies, caves, sinkholes, and underground drainage—all the result of carbonation-solution. The best-known caves are at Postojna. The barren nature of the plateau deters human settlement. Rough pasture or forest covers much of the surface, and there is little arable land. The term karst is used to describe any area where similar geological formations are found.