Oh, good point about the mask.

Thank you.
The ridgeline is on its own transparent layer. I did bumpmap the layer, but I also have an un-bumpmapped, also transparent layer saved just in case. I tried filling the layer with gray, but the selection is feathered and so it leaves a little halo around the base of the mountain.
Also, if you put the ridgeline on a layer of gray, how do you get the color? A base? In the bumpmap? My knowledge of what I can do with gimp is very, very spotty. I just figured out how to install scripts this past weekend, even. Sorry. And thank you.