Thanks Pescado - as a tip to anyone else with this problem, fiddle with anything within sight range of the artifact. The shoreline causing the problem was further down the triangle than is visible. Turn on the "View wireframe" option and trace the triangle to its base, then just mess with sloping, flattening, etc. until the artifact disappears. It was very finicky and came down to less than 5 squares that needed adjustment. There were no visible glitches, so it's trial and error to locate the offending land mass.

I have been slowly figuring out CAW thanks to posts here and elsewhere, but am having a problem. I haven't seen this reported anywhere - if it is, please let me know and feel free to delete this thread.

I have a large triangular shaped artifact that I cannot get out of my world. It appears in CAW and in Edit in Game. I had a couple others that I managed to get rid of by deleting misplaced rapids or distant terrains, but I can't seem to find what is causing this one. Any ideas?

(look in the upper left corner of the world.)