Problem with join

[cwreckord (Courtney Reckord)]

I used the cage edit to modify one end of a surface. Although I did not edit any of the points near the original surface, I can’t seem to rejoin them to make a watertight surface. I appreciate any advice!
Thanks
Courtney iceland ring small.3dm (6.3 MB)

[Derek_Heming]

If you use the ShowEdges command and click on Naked Edges it will show you where the problem area is.