At the height of the crop circle craze, this Mandelbrot Set appeared one night in a cornfield a few miles south of Cambridge, UK. Although the pilot, quoted below, thought the sight quite extraordinary, subsequent correspondence in the same newspaper soon explained the fractal pattern.
Cambridge Weekly News, 15 August 1991
The proximity of the University of Cambridge, and the time of year summer vacation seems to implicate graduate students in this case.
I do so love the way all these elaborate crop "circles" are oriented along the tractor lines and the way the pseudoscientists and alien apologists never seem to find this in the least bit suspicious.