Abstract: Accumulation of alluvial fan deposits of Köprübaşı, wich is a part of a fluvial sistem in the Köprübaşı basin, is contemperanous with Miocene block faulting. Under the control of this growth - faulting type tectonism, thick fluvial deposits having a wide range of material size from large blocks to clays have deposited. Alluvial fan deposits consist of boulder conglomerate unconformably resting on the metamorphic rocks at the base and,upward the section, Lower conglomerate with relatively small pebbles; sandstone interbedded with mudstone, silstone and conglomerate lenses; middle conglomerate; siltstone - mudstone and upper conglomerate underlying the lacustrine unit consisting of varicolored mudstone at the base and white cherty limestone at the top.These alluvial fan deposits consist of quartz, feldspar, mica garnet, clay, rutile, zircon, tourmaline, ilmenite, magnetite, pyrite, siderite, jarosite and apatite. Clay minerals in alluvial fan deposits are dioctahedral smectite and illite.Dioctahedral smectite has developed usually around small pebbles or grains as vitreous films and its dark green coloris striking. Illite is mostly detrital in origin. In some instances, the illite develops on feldspars as small flakes. Chlorite is detrital or occurs authigenically on biotites.Authigenic clay minerals occurring in the alluvial fan deposits reflect a silica-rich, slightly alkaline groundwater.