oftentime, folded rock masses get busted up by erosion, gravity, quakes etc. Then the rock get tumbles in streams for millennia. The folds are of a type called" Ptygmatic", Ive seen stuff like this in the field (Im an old field geologist ) , and ithout looking at it more closely, Im giving this as an educated guess.
I dont think they are artifacts but they have such a net story, Id urge you to take em to some college with a geology program and either donate or sell them to their museum.
to a geologist they are a really good teaching tool.