A bit of messing around with some DEM (digital elevation model) and came up with some visuals of the lower Nooksack River in northwest Washington. By shifting the elevations of the colors one can enhance features that would otherwise be hard to see.
The first image shows the complicated story of part of the Nooksack River and some late ice age drainage patterns. The dark green is lower elevation. The Nooksack flows towards the west into a broad valley formed by an older late ice age drainage. The low area on the north edge of the map is the Sumas Valley. A tongue of ice sat at this location and left the low area with its associated outwash plain to the southwest. The Nooksack flows into the area between these two low areas and for now flows west, but during big floods on the Nooksack water floods towards the Sumas.
Closer view of the Nooksack showing an elevated flood plain area on either side of the river (yellow-green) that has built up. Indeed, the low area north of the river floods deeply and takes a long time to drain.
During the late stages of the last glacial period lobes of ice blocked the flow of the Nooksack River and the river cut channels through the upland areas leaving behind coulee like features in the headwaters of what is now Ten Mile Creek in the center of the map.
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