RobA's Artistic Regional Map in Gimp Tutorial - Revised Presentation

[GunbladeKnight]

Thank you to both RobA and Whitemoon for the original and revised tutorials. However, I am on step 40 of the second PDF (editing deserts) and am wanting some clarification. It states you can add in the deserts by coloring on the layer mask with a soft brush at 60%, but it does not specify which layer mask to edit. Is it the dirt layer mask, grass bumps layer mask, grass texture layer mask, or the grass layer mask? The most current layer would be the original sketch (if you had one) which had been moved to the top.

I have also attempted the mountains before and had a similar problem as the previous posters. I am using GIMP 2.8.2

EDIT: I think the mountain problem was because it was easy to miss where you are supposed to change the output levels as well as the input levels on step 19 of the third PDF (altering the color levels on the mountain noise layer).