Jonathan,
gradient mask (i name it like that anyways) is an approach for gradually applying any correction at one side of image with little or no change to the other side.
The way you could do that is:
- press 'q' to get into quick mask mode.
- press 'd' to reset colors to default
- click on the gradient tool, make sure "linear gradient" is selected.
- click on the gradient selection, where gradients of different colors could be selected. This is at the very top left corner of PS7 toolbar. Here you're interested in monochromic gradient named "foreground to background". Just click on it to make it active gradient.
- paint gradient quick mask right over your image (still in quick mask mode) drag left mouse button to paint quick mask gradient form left to right. You'll see reddish gradient painted.
- press 'q' to exit quick mask mode - and you'll see selection. Depends on the direction of change you want - you might need to repeat it all over drawing in quick mask mode in opposite direction.
- once you exit quick mask mode and got your gradient selection "marching ants" ready - create any adjustment layer (in case of this picture - curves).
- This new curves adjustment layer automatically picks the gradient mask you created.
- touch up the contrast with curves. This will have full effect in one side of the image but gradually diminishing to zero effect in opposite corner.

That's it.

PS: With sky i did "select->color range" for sky pixels, then feathered it with value of 2, then made sure no one image pixels (but the upper sky and mountains area) is selected. Another curves adjustment layer - and mountains contrast is enhanced.

Hope it helps. Best regards,

Gleb Esman
gleb@objectiveart.org

Jonathan Lee wrote:
> Gleb,
>
> I love what I saw when I was at Grand Tetons. It was just better
> than I hope. I wish my photo skill had been better to correctly
> capture its beauty to the fullness.
>
> I really like the green enhanced on those trees left hand side and
> the sky. I am new to the concept of gradient mask and can't find a
> good step by step on it from the books I've got. Would you kindly
> elaborate or point me to a tutorial web site/book on this topic?
> Many thanks.
>
> --Jon.