I'm looking for a word that describes the way mountain ranges fade into the distance, ridgeline after ridgeline, finally merging with the sky.

I don't know of such a word but agree that we need one. An artist named Markgraf(sp?)does wonderful prints of local scenes like this.

In Rennaisance painting there is a term "sfumato", which refers to the fading of objects/landscape in the distance. Granted, I have usually heard it used in reference to the overriding colour - brown in the foreground, green in the middle ground, blue in the distance.

Now that woulda made a good subject for pork laving.

But we'd have had a disagreement on pronunciation. You say sfumahto. I say sfumayto.

Thanks Elizabeth! This looks like a good possibility, though perhaps there are other candidates for this word? At any rate, here's what the Oxford English Dictionary (online thru my local library) has to say about sfumato:
See quot. 1869.) Also as n., the technique of softening outlines and allowing tones and colours to shade gradually into one another; a softened outline or hazy form produced in this way. 1847 Manual of Oil-Painting 126 Sfumato. Painted with a light, vapoury touch. 1869 EASTLAKE Mater. Hist. Oil Painting II. 206 Another quality which was adopted from Leonardo..was the ‘sfumato’ system the imperceptible softening of the transitions in half-tints and shadows.

Why does sfumato make me think: smokiness?

Why does sfumato make me think: smokiness?

Because in Italian fumare 'to smoke' and sfumare 'to fade, evaporate' are both related. The latter has a prefix s- prepended.

Also, it is well known among art historians that Leonardo would go through a couple of packs of Camels a day when working on a painting.

Those aren't packs, those are herds or droves of camels, aren't they?

And even then there was an anti-smoking league, who would ask Leo if he thought it was Kool to smoke at the Matinee. No Craven, he would snap back "You bet your Sweet Cap it is."

I think it is a herd of Camels, says she, Hedging her Bensons....

Sweet Cap He sure is!