Hi Mark -

> What I really wanted was a surface that curved down into the
> "valley", so to speak, not up over the "mountain", which is what
> the curve that you created does.

So that means that you want to do the same construction that I showed above, but with a 2D profile from the other direction.

Note that if you look at your curve, it has a 2D profile in both the Back and the Left side viewports like this:



So it is possible to pick between 2 different 2D profiles to build the extrusion - I happened to pick the one that seemed to match the direction that you used to cut off the top of the solid.

If you want to do the other direction, you will need to create a 2D curve flat in the other view and then extrude that one instead.


> Is it possible to do what I'm trying to do?

Yes - but there is no special command for it, just like a lot of things you may need to piece together what you need by using several existing tools. If there was a special tool for every single kind of different surfacing situation, that would mean there would be 100 different tools in a huge menu that would be nearly impossible to navigate.

To get what you need in this case you need to slice the 3D curve into exactly half and then flatten it down to 2D to get the 2D profile curve to extrude.

- Michael