Interaction between large-scale tectonics of the Himalaya and the Indian summer monsoon play a major role in shaping drainage systems of major Himalayan rivers. In this study we attempted to track the sediment sources of the Neogene‒Quaternary fluvial deposits of the Kasauli Formation and Siwalik Group in the Subathu Basin of the Western Himalayan foreland basin. The depositional interval of these deposits spans from middle Miocene to Pliocene which overlap with the onset of Indian monsoon and its influence on the denudation of Himalayan rocks. Provenance analysis based on our detrital zircon U-Pb geochronology and bulk rock Sr-Nd-Hf isotope data indicates that these Neogene‒Quaternary rocks record chiefly the exhumation of the Higher Himalayan Crystalline Sequence. However, at recurrent intervals within the Siwalik Group the presence of zircon population 40–110 Ma in age suggests a sediment sourcing from the Trans Himalayan batholith. We propose that the Sutlej River that originates in south Tibet acted as a transverse paleodispersal system and routed these arc-derived sediments to the Himalayan foreland basin via one of its extinct paleochannels. Zircon data suggest that this across-orogen routing system was particularly effective during the deposition of Middle Siwalik Formation (ca 11- 4.5 Ma), when the rate of uplift of the Himalaya decreased. On the other hand, the small-scale fluctuations in the presence of the Trans Himalayan zircons observed in the Lower and Upper Siwalik formations may primarily reflect climatic forcing, which induced changing monsoon precipitation and the Sutlej’s transport capacity between dry and moist periods.