|Mima mounds in western Washington as seen from the air.|
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Research hypothesizes the earthen mounds (eight feet high and 30 across) in Washington state are probably the handiwork of gophers toiling during a 500-700-year span.
"What's really cool about this is scaled by body size, these are the largest structures built by any mammal not including humans," Gabet told LiveScience's OurAmazingPlanet. "In terms of effort, it would be like a single person building the pyramids."