Cenozoic nonmarine sedimentation within and adjacent to the Cascade volcanic arc has produced a varied depositional record. Eocene to early Miocene volcaniclastics accumulated to at least 3 km thick in a longitudinal trough coincident with the arc. Increasing constructional and tectonic relief in the Cascades during the Neogene resulted in development of volcaniclastic aprons adjacent to the arc that grade sourceward into volcanic sections. Quaternary sediments are largely restricted to terraces within valleys near the volcanoes. Neogene and Quaternary aggradation represents the impact of large eruption-related sediment loads on fluvial systems. There are three notable departures from existing fluvial facies models exhibited by these deposits. First, facies representing processes intermediate between more familiar dilute stream flow and viscous debris flow are important components of these sequences but have not been adequately described in the literature on fluvial processes. These hyperconcentrated flood-flowdeposits are frequently produced by dilution of debris flows in stream channels, and their recognition is critical to successful evaluation of volcaniclastic sequences. Second, the volcaniclastic aprons and terraces contain considerable thicknesses of debris-flow and flood deposits for which existing models would suggest arid alluvial fan settings, but lateral grain-size variation, paleocurrent data, and paleogeographic considerations fail to support the presence of alluvial fans. Debris flows and floods in volcanic areas are more voluminous and cover much larger areas than alluvial fan counterparts and are not restricted to fan setting or arid climate. Third, aggradation occurs during short periods when eruption-produced sediment loads choke streams with debris and is separated by longer periods of nondeposition and incision. Thus, little or no record of inter-eruption sedimentation occurs and biases evaluation of fluvial style.