Travels in Cascadia: Burial Mounds of the Kings of the Rohirrim? The Mima Mounds of Washington

NOTE: If this post seems familiar, it should be. I posted it just a month ago. I'm re-posting (with minor changes) to place it in the proper order of the current blog series. 

One of the vivid images in my mind of the Lord of the Rings Trilogy was the resting place of the Kings of Rohan. They were buried in mounds, and the mounds were covered by the white flowers called Simbelmynë. I couldn't help think of the Kings of the Rohirrim when we arrived at the Mima Mounds Natural Area Preserve near Tumwater, Washington.

When European settlers reached the region, some of them thought that these unusual features were indeed Native American burial mounds. But when no further evidence could be found supporting the idea, they looked for other explanations. And didn't find many...

The things we don't know about our planet are, well, not known. But geologists are the first to say that the unknowns are legion. Many aspects of Earth are still a mystery. Lots of the mysteries lie hidden deep in the crust and mantle, or on the deepest parts of the ocean basins. But some mysteries are still right there in front of us, and mima mounds are one of them.

Mounded topography forms in a number of places across the central and western United States in a number of different geological environments. Although they share some similarities, it is possible that they originate from several different processes. Ideas range from the mundane to the exotic (and unlikely). Most of them occur when a fairly thin layer of soil covers a harder layer or substrate underneath. They tend to be just a few feet high, and occur in concentrations of 8-10 per acre.

The mima mounds of Washington formed at the edge of the massive ice sheet that covered most of Canada and parts of Washington as recently as 12,000 years, and so some hypotheses involve glacial meltwater, or subsurface glacial activity. Some suggest erosion of sediment from around concentrations of vegetation. More esoteric explanations involve disturbances from the vibration patterns of major earthquakes.

Occam's Razor states that among competing hypotheses, the ones that make the fewest assumptions are more likely to be correct (sometimes inaccurately described as the simplest answer is always the best). One of the more reasonable explanations for the mounds may be simply rodent activity. When pocket gophers dug into the shallow soils and encountered harder sediments, they tended to build up the mounds, and the process continued through thousands of generations. Maybe. And maybe it's aliens...

I managed to catch a photo of the mima mounds on approach to SeaTac a few years ago.

In any case, it's a fascinating place to visit. Several trails wind their way through the mounds, and there is an interpretive kiosk with a viewing platform. It is a beautiful prairie setting, with the tweeting of birds, the buzzing of insects...and an air of mystery.

I've been to the mounds in Washington twice, and the first time was in the dead of winter when no flowers were present. This time it was summer and it was a thrill to see the fields of flowers, bringing to mind the tombs of kings and the Simbelmynë.

If you want to visit the site, here are the directions from the park website:

From southbound or northbound Interstate 5, take Exit 95 and turn west on Highway 121 (Maytown Road SW) toward Littlerock. In Littlerock, continue west (forward past the school, past the intersection with Littlerock Road that curves south, and past the mini mart/gas station on the right) onto 128th Avenue. Travel about 0.8 mile where 128th Avenue ends at a 'T.' on top of the hill. Turn right onto Waddell Creek Road and travel about 1 mile. The entrance to Mima Mounds Natural Area Preserve will be on the left. A Washington State Discover Pass is required for parking at this site.

Postscript: Dustin commented when I posted the original last month, and these ideas have some merit...

Great features! My guess is that the mounds developed when glacial outflow preferentially eroded the fissures created by patterned-ground permafrost in a periglacial environment. This photo shows mounds forming from patterned ground in Alaska.

 https://en.wikipedia.org/wiki/File:Alaska_patterned_ground_1973.jpg 

In the case of the Mima mounds, if patterned ground was originally present with hard and frozen polygon centers, and margins/edges that were soft and thawed, then water flowing over the patterned ground would preferentially erode the fissures, while being less destructive to the polygon cores. Sustained flows would likely erode all evidence of patterned ground, but the Mima mounds were likely formed from ephemeral flow events associated with glacial melt near the ice sheet margins. This type of environment is suggested by the kettle lakes visible in the upper right of your airphoto, and the mounds being distributed amongst relict braided river patterns.

Burial Mounds of the Kings of the Rohirrim? Got a Better Idea? The Mima Mounds of Washington

One of the vivid images in my mind of the Lord of the Rings Trilogy was the resting place of the Kings of Rohan. They were buried in mounds, and the mounds were covered by the white flowers called Simbelmynë. I couldn't help think of the Kings of the Rohirrim when I arrived at the Mima Mounds Natural Area Preserve near Tumwater, Washington yesterday.

When European settlers reached the region, some of them thought that these unusual features were indeed Native American burial mounds. But when no further evidence could be found supporting the idea, they looked for other explanations. And didn't find many...

The things we don't know about our planet are, well, not known. But geologists are the first to say that the unknowns are legion. Many aspects of Earth are still a mystery. Lots of the mysteries lie hidden deep in the crust and mantle, or on the deepest parts of the ocean basins. But some mysteries are still right there in front of us, and mima mounds are one of them.

Mounded topography forms in a number of places across the central and western United States in a number of different geological environments. Although they share some similarities, it is possible that they originate from several different processes. Ideas range from the mundane to the exotic (and unlikely). Most of them occur when a fairly thin layer of soil covers a harder layer or substrate underneath. They tend to be just a few feet high, and occur in concentrations of 8-10 per acre.

The mima mounds of Washington formed at the edge of the massive ice sheet that covered most of Canada and parts of Washington as recently as 12,000 years, and so some hypotheses involve glacial meltwater, or subsurface glacial activity. Some suggest erosion of sediment from around concentrations of vegetation. More esoteric explanations involve disturbances from the vibration patterns of major earthquakes.

Occam's Razor states that among competing hypotheses, the ones that make the fewest assumptions are more likely to be correct (sometimes inaccurately described as the simplest answer is always the best). One of the more reasonable explanations for the mounds may be simply rodent activity. When pocket gophers dug into the shallow soils and encountered harder sediments, they tended to build up the mounds, and the process continued through thousands of generations. Maybe. And maybe it's aliens...

I managed to catch a photo of the mima mounds on approach to SeaTac a few years ago.

In any case, it's a fascinating place to visit. Several trails wind their way through the mounds, and there is an interpretive kiosk with a viewing platform. It is a beautiful prairie setting, with the tweeting of birds, the buzzing of insects...and an air of mystery.

I've been to the mounds in Washington twice, and the first time was in the dead of winter when no flowers were present. This time it was summer and it was a thrill to see the fields of flowers, bringing to mind the tombs of kings and the Simbelmynë.

If you want to visit the site, here are the directions from the park website:

From southbound or northbound Interstate 5, take Exit 95 and turn west on Highway 121 (Maytown Road SW) toward Littlerock. In Littlerock, continue west (forward past the school, past the intersection with Littlerock Road that curves south, and past the mini mart/gas station on the right) onto 128th Avenue. Travel about 0.8 mile where 128th Avenue ends at a 'T.' on top of the hill. Turn right onto Waddell Creek Road and travel about 1 mile. The entrance to Mima Mounds Natural Area Preserve will be on the left. A Washington State Discover Pass is required for parking at this site.

Saturday's Mystery Photo Revealed: They're Mima Mounds!

Scale is everything. This morning's mystery photo could have been on another planet, a satellite image of somewhere on Earth, a few inches across, or microscopic. Without scale, we can imagine just about anything because symmetry exists at all levels. I've seen dinosaur skin impressions that looked just like the image I posted. I've also seen Mars images that resemble these as well.

Aerial shot of the Rocky Prairie mima mounds from a Seattle flight several years ago.

The photo yesterday is an image of several dozen acres of prairie in the Puget Sound region of Washington State. They show an unusual surface feature called Mima Mounds (as correctly guessed by several commentors). They're showing up in today's post because I finally had the opportunity to visit the original examples. I've discussed mima mounds in the past, because we have superb examples of them in our own home region of the Central Valley of California.

Mima mounds are found over a fairly wide area in the southern Puget Sound region, but many of them have been plowed over or covered by forest growth. A few small areas have been preserved as Natural Area Preserves or parks, most notably at Mima Mounds Natural Area Preserve (the site we visited yesterday) and Rocky Prairie near Offut Lake.

The mounds are a few feet high, several yards across, and are spaced rather evenly across the prairie surface. Their origin is still a bit of a mystery: early European explorers thought they were Native American burial mounds, some geologists feel they may be an unusual manifestation of seismic waves, and many explanations involve glacial outwash erosional or depositional processes (the prairies lie just south of the where the great continental ice sheets of the last Ice Age ended). Permafrost thawing and freezing has been suggested. Marvelous arguments have been marshaled for most of these hypotheses, but the issue is far from settled.

As I've mentioned in previous posts, some researchers suggested that the origin might be a bit simpler (remembering Occam's Razor: among competing hypotheses, the hypothesis with the fewest assumptions should be selected). They suggested generations and centuries of activity by ground squirrels or gophers resulted in the formation of the mounds. In the prairie environment, the mounds would give the rodents a better view of approaching predators, and their burrows would stay drier, being above the impermeable clays.

There is some current research on the origin of these enigmatic mounds by Manny Gabet at San Jose State University that supports the gophoer hypothesis. Generation after generation of gophers, building their mounds in the same place over time, could produce features like these in 500 to 700 years. Gabet doesn't insist that this is the absolute explanation for all mounds, but the computer modeling provides strong support for the idea.

Because the mounds occur in some conditions that are similar (prairie-type environments), but with some important differences (periglacial environments versus warmer temperate dry prairies), I find the pocket gopher argument the most compelling, as they are native to each of the environments, and apparently the mounds are of a size similar to gopher territories. I have to also say that the question is still wide open, as some important confirming evidence is not present, such as the presence of active gopher colonies on the mounds today.

In the meantime, I enjoyed wandering through the original mima mounds. They are just west of the town of Little Rock south of Olympia, and are only a few miles off of Interstate 5. There are some nice paved trails around the mounds, and an excellent interpretive display with a second floor lookout. 

The Native Americans used fire to keep the forest from encroaching on the prairie environment, and present park policies are using a variety of management tools to maintain their historical appearance. One interesting species in the area is the Garry Oak, or Oregon White Oak (Quercus garryana), the only oak species found in the state. The oak is usually quickly overrun by fir trees, but can thrive in the prairies.

As one might expect, wildflowers are diverse and widespread during the right time of year.

The park provided a nice respite from the long slog down Interstate 5. We're on the home stretch of three weeks on the road, but now it's just Mrs. Geotripper and myself. Our students have scattered to the winds, and we are only responsible for ourselves for the next few days. The story of our adventures in Canada will begin soon!