Thanks for this Jeff. I could swear I tried it both ways, but it obviously works. The docs are wrong though:
The rest surface. This is the “normal” shape of the surface without any waves on it. Waves deform the surface up and down away from this rest shape.
The initial surface. This is the starting state of the surface. The difference between this surface and the rest surface causes the first set of waves across the surface.
The “normal” shape of the surface, without any waves on it is the “grid1” sop. The starting state is “rest1”, (unfortunately named in my example as it's a rest SOP).
Out of curiosity, why would you want to call the deforming geo “rest” anyway? Isn't that counter-intuitive? Isn't “rest” geo normally the default, un-deformed version?