I'm a new purchaser of MoI. Many years ago, I did 3D modeling with math-based tools like POVRay, and then did some polygonal modeling. I fear that my approach to a particular problem is skewed by that polygonal mindset, so I'm looking for advice on how to accomplish this in MoI.

I have an extruded irregular shape that I want to make into something like a bas-relief mountain.

For example, I'd like to be able to move the selected vertices down the Z-axis (as shown). I understand that this would require creating new vertices, which is why I can't simply show points and then move them.






If I only wanted to do that one corner, it would be trivial to do a boolean operation. But I really want to end up changing the top surface of the extrusion into a terrain-like surface. What's the right way to approach this?

Thanks!
___Samuel___