Hi Bob,
Nice POV

I'll keep you up to your promise though

The bushes look good, but I'd find a replacement for the ones closest to the camera.
They have a bit wrinkled paper look and not much detail.
In the terrain group where all the displacements are made you'll see a distribution shader which limits the height of the displacements to the top of the canyon-walls.
You'll have to slightly lower this number (say increments of 5m for starters) to get rid of those disc shapes. I thought/tested it was alright, but seemingly not everywhere.
In a case of this kind of direct lighting you might decrease the addition of AO to the scene, maybe even completely delete it.
I'd love to see this rendered a bit smaller and then with more atmo samples and maybe increased GI (if you ditch the AO).
Very nice work nonetheless and I'm really happy you're using this at the moment and having fun with it

Thanks for showing!
Cheers,
Martin