Abstract Significant attributes of the Kosi fan are its flat surface, fine-grained, highly bioturbated sediments, perennial water saturation, and abundant abandoned channel facies. Pre-existing drainages controlled fan shape, and disparate monsoon and dry season discharges cause some channels to be vegetated and muddy while simultaneously containing sandy point bars. Similar fans should be recognizable by isopach-defined wedges, tectonic position, bowing of grain-size isograds away from the orogen, clustering of large channels, and interfingering with interfan facies.