I do a good deal of terrain work, and were not talking mountains... ...creating sphere and tubular shapes in the terrain editor borders on impossible, even with gradients. You're better off keeping it a boolean. WAY, way less polygons. BUT, I'm sure you want it a terrain, so you can, at the very least, export it, lol.... Wish I could help more, the key is gradients, but that is also the problem, it's very, very difficult.

Contact Me | Gallery | Freestuff | IMDB Credits | Personal Site
"I want to be what I was when I wanted to be what I am now"