I have this file in an old mod folder and I can't identify what mod it is, or where to download it again.

That's http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7039, which makes the road from Balmora to Caldera a lot more interesting by adding rock formations. It's a tiny little atmospheric mod that does its job wonderfully. It never leaves my game.