Okay, i went to search and found examples.
A crop circle pattern.
Two fairy rings marked by uneven grass growth -- no mushrooms showing -- in a school field in Scarborough, Ontario, Canada. Date: 7 May 2006.
Crop circles are geometrical formations of flattened crops found in England and elsewhere. They have been found in wheat, barley, canola, rye, corn, linseed and soy.
The phenomenon itself was observed in its current form after notable appearances in England in the late 1970s. Various explanations were offered for the phenomenon, which soon spread around the world. In 1991, two men named Doug Bower and Dave Chorley revealed that they had been making crop circles in England since 1978 using planks, rope, hats, and wire as their only tools. Circlemakers.org, a UK-based arts collective founded by John Lundberg have been creating complex crop circles since the early 1990s.
History of crop circles
1678 pamphlet on the Mowing-Devil.The earliest recorded crop circle is depicted in a 17th century woodcut called the Mowing-Devil. The image depicts a strange creature creating a circular design in a field of corn. The pamphlet the image appeared in states that the farmer, disgusted at the wage his mower was demanding for his work, insisted that he would rather have "the devil himself" perform the task.
A more recent historical report of crop circles was published in the journal Nature in 1880 (reproduced in 1991). An amateur scientist named Brandon Meland described a field containing a number of crop circles, along with the suggestion that they might have been caused by "some cyclonic wind action".
More information:
http://en.wikipedia.org/wiki/Crop_circles