D1-3 is relatively common, but typically occurs as small wetlands (thus barely visible on the range map, above) north of Clam Gulch.  D1/3 units are a combination of open water emergent and shrub communities, if sedge communities (D2) are also present, and they typically are, the unit is named D1-3.  D1-3 units are almost always segregated as a central pool or pond ringed by a sedge dominated community with a shallow water table, then by a shrubby community, or sometimes a bluejoint grass stand, with a deeper water table.  A wet forest (D4) is also usually present, but does not cover more than 10% of the depression, and therefore is not included.  Often, the forested transition from the edge of the depression to upland is rapid and steep.   D13 wetlands represent a pond ringed by an often narrow bluejoint or shrub-dominated band with a rapid transition to a steep upland.  Depressions are most common on younger glacial surfaces, such as the moraine between Nikiski and Sterling, and also east of Sterling.