Since 1841, many have wondered what might have created "Mima mounds," the mysterious (and quite numerous) large, ancient bumps emerging from the ground in Washington state's Mima Prairie. Earthquakes? Floods? Glaciers? Aliens? Nope. Most likely, it was ... gophers. Researchers think they've finally figured it out, LiveScience reports: Pocket gophers burrow into the earth, and over the years, they push small amounts of dirt, rocks, or dead vegetation above them in an effort to keep dry until—many, many generations later—you have an 8-foot-tall, 30-foot-wide mound.
Researchers ran a computer model and used "digital gophers" that behaved exactly as real pocket gophers do, the lead researcher tells the BBC. (Other types of gophers push material downward, not upward.) The model showed that after 500 to 700 years, the gophers' normal burrowing would result in the huge mounds—which are, the lead researcher says, "the largest structures built by any mammal not including humans" when scaled by body size. "In terms of effort, it would be like a single person building the pyramids." A Mima mound expert says that while the study isn't absolute proof pocket gophers are responsible, it certainly shows that the animals are capable of the feat. Mima mounds aren't specific to Washington; in fact, they're found on every continent but Antarctica. The same can't be said for gophers, but researchers speculate the mounds could have been formed by other burrowing mammals, the Sky Valley Chronicle notes. (Another mystery is closer to being solved: What happened to the missing colonists of Roanoke Island.)