The oldest rocks belong to the Werfen layers and were deposited some 250 million years ago. Most of the surface is covered by carbonate rocks, i.e. limestone, limestone with chert and dolomite. The region has many deposits of mineral resources which (especially the copper ore) led to the first settlements in Bohinj.
The remains that were left behind by the glacier are geologically the youngest (characteristic U-shape, seen especially well in the Upper Bohinj Valley). Limestone sediments (glacial moraines) and steep gorges. Throughout the centuries, the waters of Bohinj have carved wonderful channels that go as much as 20 m in depth and narrow to as little as 1 metre in some places (the channels of Mostnica, Ribnica, Jereka and Grmečica).