Yep - that's a giant crop-circle ad for Papa John's Pizza (whole wheat crust pizza ad in a field of wheat? My, what a metonymy! Wait, or is it metaphor?). Anyways, here's The Fire Wire blog has the story:
Look, it’s a bird, it’s a plane - it’s a pizza?
That’s right, it’s a pizza. If you’re flying in or out of Denver International Airport, look out the window and you’ll see a pizza cut into a wheat field near West 128th Avenue and Pena Boulevard. The crop circle, designed by artist Stan Herd, is a promotional vehicle for Papa John’s Pizza.
The pizza’s “pepperoni” is made of cedar mulch, with cornstalks standing in for green pepper, black mulch for olives, and flattened wheat stalk for cheese. It will be completed in time for the convention and will remain in place until the first snowfall.