CN's dirtiest

The hardest working units aren't running the country's mainlines, they're in the yards switching 24/7.
You're looking at a typical CN hump set:
GP38-2 mother lead (CN 7500 even)
HBU-4 hump booster unit aka slug (CN 500)
HBU-4 hump booster unit aka slug (CN 500)
GP38-2 mother trail (CN 7500 odd)

When I railfanned in Winnipeg from 2003-05 I managed to visit every yard and hotspot, except for Symington, since it was pointless trying to see anything with my old digital (3x zoom). So when I was driving back west, cross-country to Saskatoon with my new digital (10x zoom), this yard was the only place I stopped by and the only photo I took in the city.

On a sad note, the hump that this "so ugly it's beatifull" set is operating on, closed down a few days ago, since it has been decided to convert Symington to a conventional yard layout, not the big city hump yard that it's famous for.

PS. You can see the North track of CN's mainline from Thunder Bay in the foreground.