It's a grey scale image so I'd stick to black and white.
Personally I start on a black background and use a white airbrush to create the peaks. But you could work from white to black if you wanted.
Then I add a bit of noise to it to dirty it up.
See how that looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
...Once it looks right...
Slap the heightmap through terrain shader (see my sig) to light, texture and shadow it.
Get a noise map.
Slap it all together.
Then I go have a cup of tea.
Personally I start on a black background and use a white airbrush to create the peaks. But you could work from white to black if you wanted.
Then I add a bit of noise to it to dirty it up.
See how that looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
See how it looks in blitz.
Monkey around with it some more.
...Once it looks right...
Slap the heightmap through terrain shader (see my sig) to light, texture and shadow it.
Get a noise map.
Slap it all together.
Then I go have a cup of tea.