Lithology, channel geometry and bed sediment organization

Sediment transport and channel morphology in headwater, hillslope‑coupled streams reflect both hillslope inputs and in‑channel processes, but the role of lithology in shaping these patterns is not well understood. We compared two gravel‑bed streams in the Oregon Coast Range—one in sandstone and one in basalt—to examine how rock type influences channel form, grain size, and transport capacity following major landslides and debris flows in 1996. Both streams showed early downstream coarsening driven by strong hillslope coupling, but subsequent fining differed by lithology. Despite these contrasts, surface grain size closely tracked shear stress, indicating hydraulic sorting independent of rock type. Our results suggest a shared cycle of post‑disturbance adjustment, with sandstone channels more prone to gravel depletion and bedrock exposure, while basalt channels retain threshold‑like behavior longer due to more durable clasts.