New radiolarian data from the polymict Excelsior Gulch conglomerate (Wallowa terrane, Blue Mountains Province, Oregon, USA)allow narrowing the age of the chert components. Chert clasts sampled at three distinct localities yielded radiolarians that have Middle to Late Triassic ranges. Individual taxon ranges allow for the distinction of four continuous substages: early Ladinian (presence of Triassocampe nishimurae and T. postdeweveri), middle Ladinian (with Pseudotriassocampe hungarica), late Ladinian (presence of Muelleritortis cochleata and Tritortis kretaensis), and early Carnian (with the co-occurrence of species such as Muelleritortis spp. ex. gr. M. cochleata, Tritortis dispiralis, ?Corum delgado and Triassocingula perornatum). The reworked chert clasts represent Middle to Late Triassic Panthalassan open ocean sediments that have not been described in the Blue Mountains Province.