If a Terrain (2D height map) is made "solid", it can be used as a negative in a boolean group. I would guess this is how I would use it if I wanted to 'impress' the crop circle another mesh that was acting as the crops, without leaving a total void within the actual cricles (as the negative Terrain could be raised or lowered)

Additionally, a negative Terrain grouped with a great number of low-poly grass blade or wheat looking meshes could/would give a very realistic looking crop-circled field.

AS

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