This study investigates the origin and regional tectonic implications of high-altitude Plio (?)-Quaternary fluvial deposits developed over the Bozdak horst which is an important structural element within the horst-graben system of western Anatolia, Turkey. A total of 23 deposits occur near the modem drainage divide comprising fluvial to occasionally lacustrine deposits. The deposits are all elongated in N-S direction with a width/length ratio of 1/10. The largest of them is of 13 km in length with a maximum observable thickness of about 100-110 m. Morphological, lithological, deformational characteristics of these deposits and the drainage system of the area all suggest that the deposits were formed due to uplift and southward tilting of the Bozdag horst. This tilting which is estimated as 1.2 degrees to 2.2 degrees caused accumulation of the stream load along channels flowing from south to north. All the deposits were later dissected by the same streams with the exception of one deposit which still preserves its original lake form. These deposits are of Quaternary age, which corresponds to the latest N-S directed extensional tectonic phase in the region. (c) 2005 Elsevier B.V. All rights reserved.