A lot of the external terrain generator programs use this method. Actually, all of them. I recommend GenSurf but you can easily do it yourself if you have the patience. I do it this way.
1. Create a square cube.
2. Slice it from one corner to the other in the TOP view
3. Copy these two blocks to cover the area you want
4. I PREFER NOT TO USE VERTEX MANIPULATION
5. Skew the new triangle blocks up or down in the side views ONLY
6. Continue the process so that the edges align
7. use the BEVEL texture on all sides except the top to prevent bad clipnodes