Field surveys in the 724-km2 Queets river basin on the west slope of the Olympic Mountains in NW Washington reveal basin-wide patterns of distinctive wood debris (WD) accumulations that arise from different mechanisms of WD recruitment, hydraulic geometry, and physical characteristics of WD. Individual pieces of WD in an accumulation or jam can be separated into key, racked, and loose members. Ten types of WD accumulations are identified based on the mode of recruitment and the orientation of key, racked, and loose debris relative to the channel axis. Although some types of WD accumulation have few geomorphic effects, others form stable in-stream structures that influence alluvial morphology at both subreach- and reach-length scales ranging from less than 1 to greater than 10 channel widths. In the Queets river, stable accumulations of WD directly influence channel anabranching, planform geometry, flood plain topography, and establishment of long-term riparian refugia for old-growth forest development. The classification of wood debris accumulations in the Queets river basin is based on physical observations that offer a template potentially applicable to other forested mountain regions.