Here’s a video and commentary from David Carlos, who often submits photos profiling interesting places nearby.

The Mima Mounds Natural Area Preserve near Olympia is 445 acres containing hundreds of these bumps on the ground. There’s no conclusive explanation for how they got here. Theories range from the plausible–glacial ice melted, leaving deposits of soil and rocks behind–to the improbable: gophers. Another explanation is that earthquakes caused shock waves, shifting the soil into patterns. Or, water flowed around plants, causing sediment to form mounds.

What is certain: The mounds were created over 16,000 years ago. About the mounds, Charles Wilkes, Commander of the U.S. Exploring Expedition from 1838 to 1842, said: “Being anxious to ascertain if they contained any relics, I subsequently visited these prairies, and opened three of the mounds, but nothing was found in them but a pavement of round stones.”

The mounds continue to fascinate visitors. Total, they stretch up to five miles throughout private and public land in the south Puget Sound region.

— Story and video by David Carlos