The geomorphology of the rapidly extending area of western Turkey is principally controlled by large active normal faults. The graben formed by the faults are asymmetric and about 10–20 km wide. Measurements of the rotation of Neogene sediments in the footwall of the active faults and 2–D modelling of gravity data show the extension across each graben to be about 6–10 km, suggesting that the whole region has undergone only small degrees of extension (β ≈ 1.2–1.3). The faults bounding the grabens are segmented on a length scale of 5–10 km with the segments linked by some means other than single ‘transfer’ faults. Where the footwall lithology is resistant to mechanical weathering, axial drainage is important and rivers cut through the line of the fault at the end of fault segments, producing large fans. Where the footwall lithology is less consolidated, drainage is generally in linear valleys. Major graben can have more than one phase of faulting, with the main graben bounding fault stepping successively into the hanging wall.