The DW4 bluejoint grass (Calamagrostis canadensis) dominated component is uncommon as a monotype.  When present, it often exists in a complex with other Relict Glacial Drainageway ecosystem map components, represented as a scattered or patchy bluejoint grass ground cover greater than 10 percent.  As bluejoint grass is ecologically distinct in wetlands, often indicating human disturbance, or the presence of a mineral soil, and, as it produces a distinct aerial photo-signature, it is described as a separate map component in both the Relict Glacial Drainageway and Lakebed ecosystems.

DW4 components are present along the margins of 'underfit' stream valleys, outside of the active floodplain or as small units in areas of large complexes where there is a mineral groundwater influence.  They probably indicate areas close to a mineral soil groundwater source, or disturbance, although an organic layer can be well-developed.