Are you serious? All you have to do is google it. Or wiki it. Or whatever. You can find out how to make your own!
Why do you all assume that something large and complex could NOT have been made by humans?

"Circlemakers.org, a group of crop circle makers founded by John Lundberg, have demonstrated that making what self-appointed cereologist experts state are "unfakeable" crop circles is possible. On more than one occasion, such cereologists have claimed that a crop circle was "genuine" when in fact the people making the circle had previously been filmed making the circle.

Scientific American published an article by Matt Ridley,[13] who started making crop circles in northern England in 1991. He wrote about how easy it is to develop techniques using simple tools that can easily fool later observers. He reported on "expert" sources such as the Wall Street Journal who had been easily fooled and mused about why people want to believe supernatural explanations for phenomena that are not yet explained. Methods to create a crop circle are now well documented on the Internet"

from wikipedia.org

--All you really need is love, but a little chocolate now and then doesn't hurt-- Lucy Van Pelt