There's a canyon now! I've replaced a boring piece of terrain from the original animation with a much more interesting geological structure. It's still needs work, but the overall layout is pretty good.
In this shot the Demonwing speeds through the canyon. It's got several layers which adds some nice parallax to the shot.

I love me some Art Deco infrastructure, so I added a dam. Heavily inspired by the Hoover Dam (OK, outright copied).

Procedurally modelled, the canyon is built from a whole bunch of noise functions. The actual channel is sculpted, but all the detail is mathematically derived.

A top-down view of the environment. The canyon is modelled in Houdini and the dam in Maya.