Thankyou that worked great for leaving the rails behind but now how do i eleminate the lines left behind on my surface?

Using my "special psychic powers" 😕 I'd say that you perhaps have three or more lines meeting at a common 'node'.
You are selecting two lines and trying to weld them into a curve... but of course the other unselected line[s] instantly breaks the curve where it's touching [just like what happens if you draw a line onto an arc, it 'splits' the arc!] = failure !!
Remember that you can only 'weld' a 'curve' from a set of edges that are continuously joined end-to-end, and which have no other edges touching them [except perhaps at the very ends of this potential 'curve']...
🤓

Because it's symmetrical do one half and then mirror a copy to finish.
Also group and hide all superfluous things to make life bearable.Capture.PNG
Join all curves into continuous sections [use weld.rb].
It then Curvilofts or EEbyRails OK...Capture1.PNG

In previous versions of SU, we could only import greyscale imagery. I do not see how they are of better quality than the current colour version. Sure you could reload that image with the colour version exported from GE. If that is a good solution, you can still use SU 7 or 6 to import the GE image/terrain in the old fashioned way and then go on using version 8 with modelling.

In my area, the "best" imagery is rather poor anyway so I do not see any difference.

@oneturboneeded said:

Ok now i have my 4 groups extruded by rails how do i combine into one group eliminate the lines between groups and smooth? Im just getting lazy now that you are all so helpful and guide me strait to the right operation but im learning lots thanks.

Select the 4 groups [hold down Ctrl to add to a selection, Ctrl+Shift to remove from selection and Shift to toggle in/out of selection!]
Self right-click context-menu 'Explode'.
Everything remains selected, immediately right-click context-menu 'Group'.
Everything is now in one group.
Select that group and right-click context-menu 'Smooth' - adjust the settings in the dialog that opens so it's smoothed.
If there are an edges that won't edit the group and smooth using Erase+Ctrl OR if that fails hide them using Erase+Shift...
As you have only made a 'half' you can them copy the group to one side ans Scale it -1 about Y/green so it flips.
Move the two groups so they snap together correctly, when you are happy Select both groups and Explode, re-Group, and re-Smooth as before....... 🤓

You need to have this edge and these faces insidethe groups to make them solid.

solid.png

If you want to bend some thing different than a cone try FredoScale.
See attached example

Oblique Cone Radial Tip.skp