If you’re familiar with Thurston County, you may have heard of the Mima Mounds. The Mima Mounds Natural Area Preserve is located about 20 miles south of Olympia, and it’s a nice, peaceful place to hang out and stretch your legs. It also happens to be one of Washington’s greatest mysteries.

This beautiful area includes a small Garry oak woodland and savannah, where you'll find a variety of butterflies and birds.
Brian Henderson / Flickr
The National Park Service designated this space a National Natural Landmark in 1966, and it's one of only 17 in Washington.
Right away, you'll spot the mima mounds, hundreds of grass-covered mounds stretching over several hundred acres.
Brian Henderson / Flickr
The site spans 637 acres, so it's not a small area.
The mounds are subtle, and they seem to fit right in with the landscape.
Brian Henderson / Flickr
There's just one concern: even after decades of research, nobody knows what caused them.

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At various times, scientists and researchers have formed theories about the Mima Mounds and how they were formed.
Brian Henderson / Flickr
However, virtually every theory has been proven wrong, and scientists are still baffled.
One theory is that the mounds were created by pocket gophers, which some believe to be true.
John D. Anderson / Flickr
Other hypotheses say that they formed via shock waves from earthquakes, ancient floods, or runoff from glaciers. The Upper Chehalis Tribe took a mythical approach. Long ago, one of the tribal members refused to bathe or wash her face because she was scared that something bad would happen to the Earth. When she finally bathed, it rained so hard the world flooded. When the water receded, the prairie land below took on the shape of waves.
No one knows for sure, at this time, how the Mima Mounds formed.
Jim Belford / Flickr
Luckily, they are harmless, and they give us one unique landscape.

Do you have any theories on Washington’s Mima Mounds?

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Featured Addresses
Mima Mounds Trailhead, 13549 Mima Rd SW, Olympia, WA 98512, USA