Thanks for the comments.
Andrew and Francois, you're right: AA's photograph was called Aspen. One online version of it is here
. I wasn't consciously aware of its existence but it might have been lurking somewhere in the dark recesses of my mind.
It was a serendipitous shot: I was on my way to Bright Angel point and saw it across a small field to the right hand side of the road, so I stopped. The light was catching the tree and making it stand out, although as I've found before I can't come anywhere close to reproducing the wonderful shimmering effect of those golden leaves shaking gently in the breeze.
I agree, looking at it again, that the jpeg I've posted looks rather over-sharpened, but the full file I have really doesn't. I don't know whether distance is relevant: the shot was taken using the full reach of a 70-200Lf4 on my 5d2 and it's only very slightly cropped.