Ancient UFO?

The third picture in this series was taken high up on a ridge. Looking down into the valley below I saw this fascinating structure. it makes me think of the word "kerplop". Yes, indeed that looks like flared circular shape tilted on it's side with echoes of the same for do the right. How did this form? I have no idea, but I sure would like to figure it out.

Wyoming
Geology
UFO
Odd Formation