As a bit of follow up on the DEM (digital elevation model) messing about I zoomed in a bit at the Nooksack River avulsion (course change) location near Everson.
The river flows into the image from the south across a broad braided-channel flood plain. The river then bends sharp to the left at Everson just before it passes under a State highway bridge. It appears almost delta-like as over bank deposits on either side of the river cover a broad flood plain down stream of the Everson Bridge. If you look carefully to the northeast of the bridge, meander channels very similar in size to the Nooksack River can be seen in the plain heading towards the low area left by the Sumas ice lobe during the late stages of the last glacial period. Credit to Paul Pittman who noted the meander size relations and that the meanders are too big for the streams that now occupy them. Drainage out of the Sumas low area is to the north towards the Fraser River.
This shift in the river flow opens some interesting questions: When did it happen? How? and Could it happen again and reverse back to the Sumas low area? During large floods on the Nooksack flood water does spill towards Suams making for some challenging flood modeling.
The DEM image above is built from LiDAR elevation data incorporated into the map application, but other programs that utilize all the LiDAR data could create even more sharply refined images. The above works well enough to be illustrative without taking lots of computer power or programming.