Well...Crater Lake (Mt Mazama) blew it's top. Something like 10 or 11 thousand years ago. And there is an ancient caldera, a couple million or so years old, in south eastern Oregon, that was caused by the hot spot that's under Yellowstone now. This is neither of those. If you look at ancient super volcano calderas, they look nothing like this. If you look at known impact sites, they look a lot like this. I'm not saying it is an impact site. Maybe vegetation on the ground in this photo is giving it the round shape. Although the feature on the NW side is called something or other Rim. ( I can't remember the name right now) I did look around on the internet and such and found no reference about this thing. I can't believe no one has noticed it before.
