Canyon or Ridge? Arizona Photo From NASA Goes Viral

NASA posted a photo of a satellite image with a caption: Canyon or Ridge?

On August 29, 2015, NASA astronaut Kjell Lindgren tweeted this photograph of a canyon from the International Space Station. “Flying over Arizona. Crazy how the shadows make this canyon look like a ridge!” he noted. Lindgren was noticing an optical illusion called relief inversion. The effect happens because most of us expect an image to be lit from the top left corner. When the sunlight comes from another angle (especially from the lower edge), the shadows fall in ways we don’t expect and our brains turn valleys into mountains to compensate. The problem is usually resolved by rotating the image so the light appears to come from the top of the image. In this case, does that work for you?

Here is the photo of the canyon that looks like a ridge:

Now, with a little orientation, here is the photo of the canyon:

What did you see at first, a canyon or a ridge?