once again, some little help that I need for UTNT



I'm absolutely pleased with the map and I am also very pleased with how the sky texture turned out... but I am not pleased with the pixelated and terrible looking mountains.
What I now need is a high resolution version of this:

(dark = background, light = foreground)
I have no idea how to start with that or what to do exactly but if you have some ideas, feel free to create something for me, something hi-res that looks good later and fits where these mountains are right now


Greets,
Torm