 Croatia proper straddles the boundary between the Dinaric Alps and the Pannonian Basin.The boundary of these two geomorphological units runs from Žumberak to Banovina, along the Sava River.The Dinaric Alps area is typified by karst topography, while the Pannonian Basin exhibits plains, especially in the river valleys—along the Sava, Drava, and Kupa—interspersed with hills and mountains developed as horst and graben structures.