Neil, I looked at your data, and I was able to snap to points of any elevation, not just the topmost.
I used 3dpolyline to connect the points below. Osnap set to Node.
Delta Engineering Systems
Autodesk Authorized Value-Added Reseller
Tim - I think your post prompted me to think OSNAP and I had OSNAPZ set to 1; when I changed it to 0 I was also able to use NODE to snap to locations at various depths.
Now to try and make some sense of the geology......
(No connection with Autodesk other than using the products in the real world)
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