If you are using Photoshop you use the "lasso" tool. Outline your mountain then use the fill function for 5z (or where ever you need to start) then use the "contract" feature/button (I have a macro for mountains) fill with the color for 10z.
Repeat this for as many times as you desire to get the hight you were looking for but beyond 75 is pretty much as waste.
If you have trouble reading my post you can try "Bablefish" located here;
http://world.altavista.com/
Ryandor has a tutorial located at this link on how to make mountains as well as several other people from the forums here;
http://www.ryandor.com/files/makingmaps.11.pdf
Hope that helps you.
Dev