Aliens???

Mysterious structure in my front yard

I saw this appear over a 1 hour period. It doesn't look finished. I wonder what it is...

I think the only logical explanation is aliens. First they do Stonehenge and crop circles, and now this???

At least it's comforting to see that they use simple tools like shovels, and not crazy high-tech-laser-beam-matter-changing-nuclear-light-saber-human-genocide devices. Or is the shovel there just to throw us off and lull us into a false sense of security???