In the Northwestern states of Idaho, Oregon, and Washington, there are areas filled with these small oval mounds of earth.
There are many scientific theories as to how these tiny hills were created.
My favorite theory is that they were made by pocket gophers.
One family of these rodents is estimated to be able to move up to five tons of dirt a year and the mima mounds are located in gopher territory.
This theory is debatable, but really fun to think about.