One of my favorite Martian optical illusions
Once you read this, you'll never see that image the same way.
The image is of a gentle slope. The slope exposes layers of rock, which are broken and weathered. The fracture lines are roughly perpendicular, so the blocks are roughly square. The rock itself is dark, but it's been coated in ligher material.
Try it, you'll see what I mean, especially near the bottom of the image. Once you see the blocks, you can never again see one edge of each forming a field of geysers. It's an optical illusion that's snagged a lot of anomalists over the years.
--Robert