Wrinkles on extruded surface edge

I made these levels simply by joining tangent circles to make an enclosed polyline, and extruding. Notice the selected purple one shows clean wireframe, but the faces on all three extrusions show triangular puckers: What is that and what can I do to prevent and/or mitigate that?

This looks like a display problem caused by bad meshing of an internal tangent joint (classic problem in Rhino)

When you extrude, on the command line, you should have the option SplitAtTangents. By default it is set to No. If you set it to Yes, does that help?

Another check is to run the command DivideAlongCreases (with nothing selected), set the command line option SplitAtTangents=Yes, then select the object in question and Enter. If that fixes the appearance, then that was the problem.

Since I’ll never catch up to you, I appreciate you dropping these hints that make me smarter every time. Will get back shortly with results…