Thanks everyone

Very effective, Dave. I'm curious about the colour version.
I am afraid there never was a colour version as such, as I mainly processed all the files in ACR and then stitched them all straight back together in PS under Photomerge as a mono. You see when I was taking the shots, the light spilling over into the bottom of the glen to the right, was still so hot that when I metered it as I took a test shot, the camera suggested that I should underexpose by about 2 stops, so I did. This made the images on my review screen look very dark and monochromatic and which I very much liked the look of. So as I was using a Sony sensor and people keep saying how they are supposed to be sooooo good at allowing you to lift up the details, even out of the thickest of black shadows, I decided to stick with what the camera was telling me and underexpose by 2 stops, even though the mountain sides were quite dark by this time other than where the light was hitting them and lo and behold it worked.
But I did take many shots in the glen that evening and so I do have a colour version from a short time before I took the mono shot and when the clouds seemed to be blocking out most of the hot areas in the sky.
This shot is really the result of me just having a play around and trying to create a really, really super wide pano shot. So even though this looks like a shot of Horseshoe Bend or something, it is actually a vertical orientation 180 degree stitched pano, that is so enormous that when I load it on screen, it makes the cooling fans on my computer wind up to full speed and sound like an hovercraft flying over a thin metal tray covered in rusty ball-bearings.
So I don't think I will be creating any more vertical 180's for a while

Dave