Mima Mounds

by Dawn Farmer

Last Saturday we decided to explore these strange formations in southwest Washington State. These are large uniform mounds of earth covered in prairie. These formations also go by the name Hogwallows and appear in at least six other states and five other countries.

No one has been able to determine the origins of these mounds, but the leading theory about retreating glaciers got a boost when Department of Natural Resource scientists presented new laser imaging of the mounds.

These new images make a convincing argument that these mounds were formed near outburst channels of melting glaciers. The surging melt water carried the gravel and stones that form the base of these mounds. This theory goes on to say sun cups formed (a glacier surface feature) and continuing melt water deposited more sediment. When the ice was gone these mounds remained.
My simplistic explanation provided with apologies to geologists.

Some folks think these mounds were formed by the vibrations of earthquakes, or gophers, or that they are Native American burial mounds. However these mounds formed, they are currently covered in beautiful wildflowers.

The aerial and laser images are from a Seattle Times article found here.

8 replies »

  1. This is in the SW? Near the Columbia River and the Pacific? I don’t think I ever made it farther south than Westport along the coast. Next time I’m out there, I’ll have to go check it out.

  2. JS – not that far south – in fact just past Olympia. If you decide to press on further south (and you camp) try staying at Cape Disappointment. It’s near the mouth of the Columbia River and rich in Lewis and Clark history. It’s a lovely drive down there through fishing communities and other small towns.

    I was surprised to learn this area is considered prairie, something I associated with east of the mountains. This state continues to surprise me…

  3. I’ve been as far east as Sicily, but never further west than St Louis, MO. I’d like to see these mounds before I die. Any bears there? I always thought a bear would get me in the end.

  4. Thanks Dawn. I have been to and through Olympia many, many times, and driven from Seattle to Portland pretty often, but I never even heard of these mounds. And I never heard there was prairie in Western Washington.

    As for the fishing villages, I’m betting my wife has been to all of them. She grew up a commercial fisherman’s daughter on the Kitsap Peninsula.

  5. Terry – I saw no bears – so you’ll be safe!

    Russ- thanks, the flowers were really lovely and delicate.

    JS – No doubt your wife knows all the villages – one of them is the oyster capital of the west coast. There are literally mountains of oyster shells in that town! Last time we were at Cape Disappointment I wanted to photograph Ilwaco’s marina and fishing boats, but the rain was torrential. Perhaps next time. Have you been up to the Hoh rainforest?

  6. Dawn,

    My wife says she does, in fact, know every fishing village along the way, though she doesn’t recall the mounds. She goes on to say that Cape Disappointment is well named, at least that’s the way it seemed to her as a child.

    And yes, I’ve been to the Hoh rainforest. Lovely. Have you been to the Sol Duc hot springs?

  7. JS – tell your wife my son would agree with her! I personally thought the light houses were pretty cool and I loved the hiking trails near the cliffs. My favorite camping on the coast is at Grayland. It’s easy and close. The oyster shell mounds are at Willipa Bay in South Bend, WA – heck they say oyster capital of the WORLD! 🙂 I haven’t gotten to the Hot Springs yet – but it’s on my list. It’s been a few years now since I’ve been over to that part of the Olympic Peninsula.