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!

Mima Mounds in Merced County

We were on the road today with some students, exploring the southern end of the California Mother Lode, the site of the 1848 Gold Rush. One of the first things we saw as we approached the Sierra Nevada Foothills were the enigmatic features called mima mounds.

I talked about mima mounds a few months ago, with pictures from Stanislaus county, Yokohl Valley, Tehachapi, and even their most famous site, the Mima Mounds south of Seattle and Tacoma. But someone asked at the time if I had pictures of the ones just south of where I live, which I have driven past many dozens of times, and I realized I had never photographed them. They lie south and west of Hornitos Road on the prairie lands east of the valley town of Merced. I almost missed them again today as we started on our field studies class, but I grabbed the camera just in time to snap a few shots as we sped by.

The mounds have been attributed to Native American burials, earthquake waves and other complicated causes, but the latest research suggest that thousands of generations of gophers produced them. Maybe not the most fun of explanations, but the most satisfying as far as I am concerned.

There were quite a few sights on the road today, more on them in other posts!

You Mean That Aliens Didn't Do It? New Research on Mima Mounds in the American West

Mima mounds south of Seattle, Washington

What's life without a little mystery? For years, geologists and geomorphologists have been curious about a landscape that shows up on prairie lands around the American West. It's a regular pattern of low hillocks called mima mounds. The hills are a few feet high and a few dozen yards across. They generally occur where there is a clay substrate that sometimes causes pools to collect between the mounds. These are called vernal pools, and for the few months that they hold water, they support a large variety of unique plants and animal species.

Mounds in the Yokohl Valley region in the Sierra foothills near Sequoia National Park.

The mima mounds are a mystery because their origin is not exactly clear. Early settlers thought they were burial mounds for Native Americans, but that is not supported at all by archaeological research. Some have suggested that they result from disruption of the soil by earthquake waves. The mima mounds I photographed from above (first picture) were in Washington near the margins of the vast continental glaciers, and some have speculated that they formed as a result of meltwater flooding in some fashion. Other less scientifically oriented observers suggest that aliens from space have something to do with their formations (landing pads, maybe?).

Mima mounds near Willms Road in the Sierra Nevada foothills near Knights Ferry on the Stanislaus River.

Of course, some people 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.

I was pleased to run across some current research on the origin of these enigmatic mounds by Manny Gabet at San Jose State University, and the verdict is...gophers. Generation after generation of gophers, building their mounds in the same place over time. Gabet doesn't insist that this is the absolute explanation for all mounds, but the computer modeling provides strong support for the idea. The mounds would develop after around 500-700 years.

Snow patches outline mima mounds at Tehachapi Pass in southern California (photo by Mrs. Geotripper).

Sorry, alien lovers...maybe Roswell has some new evidence.

The Other California: Yokohl Valley Drive in the Southern Sierra Nevada...and a "Blank Spot" on the Map

To be clear, the "blank spot" on the map is MY blank spot, not the cartographer's. For all the geological explorations I've been documenting here at Geotripper for the last five years, there is a frustratingly large area that I haven't set foot in for thirty years or more. It's the southernmost Sierra Nevada.

I imagine that many people miss that the Sierra Nevada continues for many miles south of Sequioa National Park, but it is a fascinating region containing a national monument, four wilderness areas, a state demonstration forest, and a county park preserving a sequoia grove. I spent some of the finest weeks of my boyhood in this region, at a scout camp (Circle B Scout Ranch; now disbanded and sold off), and on a fifty mile week-long hike through the Little Kern River Valley and Maggie Mountain. But my boy scout days were a very long time ago, and I have not managed to get back to the region since.

And that is a true shame, because the southern Sierra Nevada is one of the most beautiful parts of California. A few weeks ago, I made a brief foray into the mountains of my youth, taking an excursion along Yokohl Valley Drive, which led us from Springville to Highway 198 near Three Rivers.

The road doesn't exactly go anywhere. It's mostly there to provide access to a number of ranches, but along the way there are some gorgeous vistas, and springtime provided us with some beautiful flower displays. At our first stop, a Red-tailed Hawk watched us carefully...

The road crosses a divide at 2,700 feet, and a look east gave us a tantalizing view of some of the high country. The high peaks include Dennison and Moses Mountains, and hidden in the folds below the peaks are Balch Park (Tulare County), and Mountain Home State Demonstration Forest. The rest of the mountains are preserved as Giant Sequoia National Monument, established by President Clinton in 2000. Nearly half of the remaining groves of the Giant Sequoia trees were preserved by the designation.

Much of Yokohl Valley Drive cuts through granitic rocks of the Sierra Nevada Batholith. The hilltops show some nice examples of spheroidally weathered granite boulders.

The wildflower displays were a bit scattered in this dry year, but several sections were dappled with blue, purple and gold. The tallest plants are bush lupine, with yellow fiddlenecks filling the lower areas.

In a few scattered spots, the golden poppies dominated. It won't be but a few weeks before the flowers are gone, and the dry heat of the summer settles in.

At the bottom of the long hill I was surprised to see some mima mounds! These enigmatic low hummocks (sometimes also called "hogwallow" mounds) are found in widely scattered locations along the eastern Central Valley and western Sierra Nevada foothills. They were once thought to be burial mounds, but there is no evidence of this. Other hypotheses include preferential tunneling by gophers and ground squirrels, ancient stabilized sand dunes, heaving effects dating from the ice ages, and wave effects from earthquake activity. And aliens, of course.

I don't know which hypothesis fits best with the phenomenon, but rodents make the most sense to me. But that isn't nearly as fun as weird earthquake wave-forms.

Google Earth provides a satellite perspective on the strange mounds...

The Other California is my long on-again, off-again series exploring the fascinating geological localities that don't often appear on the tourist's postcards.

Postscript: Of course, such a beautiful place would have to be slated for development: http://www.saveyokohlvalley.org/ . I hope that since the site hasn't been updated for a few years, and there were no resorts in Yokohl Valley that I could see, maybe it has been tabled or cancelled...

The Other California: The Prairie Lands

California is known for many unique landscapes, including renowned scenery like Yosemite and the Sierra Nevada, the Big Sur coastline, or the forbidding wastes of Death Valley. There are also, of course, the urban landscapes of San Francisco, Los Angeles and San Diego. But there are some places in the state that are rarely noticed or considered. I live on the edge of one of those unique places, the prairie lands that surround (and once covered) the Great Valley province. It is a lonely region, dotted by the occasional orchard or cattle ranch. These lands, for particularly geologic reasons, were never developed for agriculture the way the Central Valley was. Wandering the backroads beyond my small village is a journey back into California's past, before the wholesale transformation of the landscape into farmlands and urban skylines.

There are several distinct regions of prairies around our valley. Farther south, near Coalinga and Bakersfield, and adjacent to the Coast Ranges, the prairies are drier and more alkaline, more nearly a desert landscape. A portion of this region has been preserved as the Carrizo Plains National Monument, which I may describe in a separate post. It is also a great place to see the San Andreas fault!

The region in which I live is a transition zone between the rich agricultural soils of the Central Valley around Fresno, Merced and Modesto, and the rocky ridges of the Sierra Nevada foothills. The underlying rocks include alluvial fans that developed as muddy rivers flowed off the Sierra Nevada block during the ice ages, and some of the volcanic lahar deposits and ash flows that preceded the glacial times. Rivers have not flowed across these surfaces for tens of thousands of years since the ice last invaded the high country. This long period of chemical weathering has resulted in the development of a clay-filled soil rich in iron oxide and hardpan (caliche deposits). The occasional winter rains that we get cannot sink far into the surface, so the primary vegetation is grass and wildflowers. A few oaks dot the higher hills.

In historic time, before the ranches, these prairies were grazed by tule elk and pronghorn antelope. The pronghorns were hunted to extinction by 1920, and the elk that roam a few isolated refuges are descended from single pair found in Kern County in the 1920's. California grizzly bears also lived here. In much earlier times, prior to about 12,000 years ago, the fauna included horses, camels, bison, mastodons, and mammoths. Giant condors flew overhead. Sabertooth cats, dire wolves and American lions hunted the grazers.

Some surfaces (as in the photo above) are covered by a regular pattern of small hummocks called mima mounds. Their origin is enigmatic, but is probably related to thousands of generations of ground squirrels occupying the same individual hills year after year. Other more exotic explanations involve Native American burials, odd earthquake waves, and periglacial soil activity.

The bottom photo shows the geological relationships in the prairie outside my town. In the foreground, the protruding rocks are part of the metamorphic bedrock of the Sierra Nevada, dating to Mesozoic time. These rocks were highly deformed and deeply eroded during the late Cretaceous and early Cenozoic, between 80 and 40 million years ago (approximate dates, and mildly controversial). The erosional unconformity is covered by ash flow deposits from about 22-28 million years ago that originated near the present-day Sierra Crest around 40 miles to the east (the Valley Springs Formation). The ash is in turn covered by voluminous lahar deposits (volcanic mudflows) of the Mehrten Formation, dating to around 9-11 million years. The lahars are probably responsible for the prominent ledges on the hillsides.

When I first came to live in the Central Valley, I didn't always appreciate the serene beauty of these wide-open landscapes. The geologist in me always wanted to see high mountains and steep-sided plateaus. The landscape has grown on me...the prairies are a special place.

And just wait til you see them in springtime. No black and white photos then! Have a good Thanksgiving holiday, if you live where it is celebrated. If not, give yourself a moment to think of the things you can be thankful for! And be safe in your travels...

Picture of the Day - The Airliner Chronicles Part 5

One more Cascades photo; one that mystifies me a little bit, as I am unfamiliar with the territory...I am wondering if anyone has a clear idea of the origin of the mounds? This shot was taken on the approach to SeaTac from the south. I am curious if they are mima mounds, although if they are it still doesn't answer the question of their origin, since mima mounds are sort of an enigma themselves. I am also curious if this picture has some subglacial features, channels or kettles.

I welcome some speculation or even some expertise!

Addendum a few hours later....researching my own post: the GoogleEarth site for this picture lies at 46 deg 54'52.13"N, 122 deg 50'21.84"W in Thurston County, WA. Looks like a classic mima mounds site, but has other interesting features too.

We actually have some mima mounds in our own backyard here in the Central Valley of California, although I am not sure if they share the same origin. Certainly no massive ice sheets here in the Merced/Modesto area during the Ice Ages, although some of the low foothills here include some outwash plains.