Trebuša is a junction of three rivers: Idrijca, Trebušica and Hotenjka. The old river courses are still visible, about 10 meters above the present riverbeds. Because of constant water activity and a typical geological structure riverbeds of rivers in the area have a normal V-shaped relief. Flowing waters, streaming from surrounding hills and plateus formed narrow gorges or glens over years.
From the above hills torrents, which are usually shorter, join streams and rivers and carve their course into the surface and have an influence on the formation and shape of larger valleys. The rivers have cut their course into the sediment. The valleys of Trebušica and Hotenja are so narrow, that there is not enough space for anything else but the water stream. The only plain terrain is at the junction of rivers Hotenjka and Trebušica and then again at the junction of rivers Trebušica and Idrijca. There are settlements on the terraces just below the steep slopes (the incline can reach up to 38-48 degrees) in the valley of Idrijca and the rough terrain offers meagre possibilities for land cultivation.
The Trebuša valley has Alpine flora (a typical representative is the primula auricula), as well as Mediterranean flora (its representatives being the daphne blagayana and the black pine, pinus nigra). Steep dolomitic slopes above the Trebuša valley and the valley itself are rich deposits of glacial floral remains, mixing with iliric and mediterranean flora. Black pines are autochtonous. Among the rare species are for example primula carniolica and daphne blagayana, and among the glacial remains primula auricular, saxifrage squarrosa, carex firma and carex ferruginea.
Interesting fact: The area of Trebuša is an important botanic area. Here mediterranean plant species mix with those species, which usually grow above the forest level.