Bounded to the east by the Dinaric Alps, which rise to an elevation of , and to the northwest by mountain Svilaja, the majority of the catchment drains calcareous rocks of Cretaceous age, predominantly limestone. Rocks of Triassic and Jurassic age also crop out in the catchment and include dolomitic limestone and flysch. The underlying karst geology controls relief with a series of structurally aligned basins separated by high ridges.