D4 map components are widespread, especially on late-Wisconsin aged moraines.  D4 is the Depression Ecosystem map component dominated by forest or woodland, with a deeper water table.  It is commonly part of a segregated complex at the forested margin of a depression, but also occur as isolated individual forested depressions.  This is the component where wetlands grade to uplands, and thus they are more difficult to correctly interpret as wetlands or uplands from aerial photography.  Often mineral soils are found here, and the only wetland indicator is a soil horizon containing redoximorphic features close to the surface. A sphagnum lawn is sometimes found in and between this and the shrubby D3 zone below it, especially north of Clam gulch in black spruce (Picea mariana) dominated depressions.

In Homer, the name D4d refers to a wetland that was a D4 but is now disturbed.