These geological anomalies are circular hillocks that cover great swathes of land. But scientists have been puzzled about what causes them.
Now new research suggests that tiny burrowing animals are their architects.
The findings will be presented at the American Geophysical Union Fall Meeting in San Francisco.
Mima mounds, which measure up to 2m (7ft) in height and 50m (160ft) in diameter, are found all around the world. However, they are most common in North America.
In some areas, they can number in their millions, stretching for many kilometres across the landscape.
Lead researcher Dr Manny Gabet, of San Jose State University, told BBC News: “The big mystery surrounding Mima mounds is that, until now, nobody really knew how they formed.
"Over the past couple of hundred years, people thought they might be Native American burial mounds, or they were caused by earthquakes or glaciers. Some people even suggested extraterrestrials."
Now though, Dr Gabet says he is certain that gophers have created the mysterious mounds.
Using a computer program, the researchers analysed how the rodents move soil as they burrow.
They found that in areas prone to waterlogging, the gophers gradually shift tiny amounts of earth upwards to try to stay dry.
Over hundreds of years, though, as many generations of gophers repeat this process, these minute piles of soil grow into the large structures.
Since Mima mounds formations can be found in various parts of the world, places that do not have gophers, where do they come from. Before resorting to extraterrestrials, local scientists might want to check for ground dwelling animals of some sort. Adding to the amazement of the cause of the Mima mounds is that it can take so many years for them to be made.