Backyard Crop Circle

We have a crop circle in our back yard. A path of beaten-down grass, three feet wide, starts suddenly near our porch, angles to the left, then makes a ten-foot diameter circle. And then it stops just as suddenly as it started.

I haven't mowed the lawn so far this year, so the grass is about three feet tall. The path I've walked to the back garden to water the new irises doesn't stay beat down anything nearly like this crop circle. It's been a couple days. The grass stalks are lying flat on the ground, like someone (or something) rolled a heavy object over them.

But where did the heavy object come from? Where did it go?

Maybe it was a giant snowball and it melted. . .