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Mima Mounds Baffle Geologists, but the Oddities Intrigue Visitors

Updated September 25, 2017.

Mima Mounds Baffle Geologists, but the Oddities Intrigue Visitors

Mima Mounds are not the roadside oddity road trippers usually encounter, but they are definitely a unique curiosity worth taking the road less traveled to see!

Located west of Littlerock Washington, southwest of the Seattle/Puget Sound region, Mima Mounds Natural Area Preserve makes for a fascinating half day trip.

Though it is off the beaten track, less than fifteen minutes from the I-5 freeway, families of all ages enjoy the mysterious scenery dotting a stunning open prairie.

Children love this place!

Set against a spectacular volcanic backdrop, the snow-capped peaks of Mount St. Helens and Mount Rainier can be seen on clear days.

Pack a picnic lunch, grab your camera and binoculars, and then get ready to spot myriads of wildlife, especially birds and butterflies.  Well maintained facilities include parking, picnic tables and restrooms.

The preserve is open year around.  To gain entry, visitors must have a Discover Pass (no pay station or passes available at the preserve).

About Mima Mounds Natural Area Preserve

The first known documentation of the Mima Mounds occurs in the journal entries of notable historical figures.

“In short the whole aspect of the plain, its sinuous banks, the larger and smaller knolls, its slope towards the Chehaylis River and the oral tradition of the natives, unite in strengthening the opinion that it has in some former period much more recent than the deluge belonged to the region of waters.”

--Sir James Douglas of the Hudson’s Bay Company at Fort Vancouver, April 1840

More historical documentation of the unusual mounds came from the journals of the United States Exploring Expedition (1838-1842), requested by then President of the United States, John Quincy Adams and later commissioned by President Andrew Jackson, following an act of Congress.

The United States Exploring Expedition was charged with exploring and surveying westward coastal lands and the Pacific Ocean. On their journey they discovered the mysterious mounds pimpling the earth in a large prairie near current day Littlerock, Washington.  

At first, they surmised the mound area might be an ancient burial ground.

“Being anxious to ascertain if they contain 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.”

--Charles Wilkes, Commander of the United States Exploring Expedition, May 20, 1841.

“This evening we encamped in the Prairie de Bute.  This is remarkable for having innumerable round elevations, touching each other like so many hemispheres . . . I travelled twenty-two miles through this extraordinary looking prairie.”

--Paul Kane, Artist-Explorer, April 6, 1847

Other historical figures followed, using their expertise to solve the mystery of the origin of the mounds.

“I would suggest that they may have been produced by eddies and whirlpools, probably at a time when this sound [Puget Sound] formed the estuary of a great river like the Columbia, or perhaps were branches of the great system of northwest sounds which extends from the Columbia River to Sitka [Alaska], or further.”

--James Graham Cooper, Pacific Railroad Surveys, 1853-1854

Like yesteryear, theories still abound about the origin of the mounds.

Are they pocket gopher mounds?

Are they naturally occurring geologic structures such as wind-blown dunes forming around clumps of vegetation or the remains of repeated shakedowns from major earthquakes?

Perhaps, the mounds are a result of wetlands upheaval or some kind of clay soil wallow-action.

We may never know the secret behind the making of Mima Mounds.

To conserve this outstanding natural site, the National Park Service designated the area as a National Natural Landmark in 1966.

Since that time, civilization has encroached on its boundaries.  Ringed by fenced-in housing developments and a shooting range, this swatch of Puget prairie grassland thrives, because of ongoing efforts to protect the rare landforms.

In 1976, it was established as the Mima Mounds Natural Area Preserve, 637 acres of mounds, forest, oak woodland and savannah, home to prairie dwelling wildlife, wildflowers, birds and insects.

Active restoration efforts continue as evidenced by controlled burns and other non-native botanical controls.

Explore Mima Mounds Natural Area Preserve

Click on the links below to find fantastic places to see and thrilling things to do!

the journey begins here . . . live the adventure!

Map Your Road Trip

Use the map below to locate the destination of your choice.  Click on the red pins to get more information.

How to Get there

In western Washington State from the north or south, drive on I-5 and take Exit 95.  Turn west onto State Route 121/Maytown Road S.W. and drive about three miles to Littlerock, Washington.  Drive forward after stopping at the intersection and continue on 129th Ave. S.W. until the road ends at a crossroad intersection.  Turn right (north) onto Waddell Creek Rd. S.W. and drive about three quarters of a mile.  Turn left at the signage for Mima Mounds Natural Area Preserve and continue to the parking lot.


After visiting the very informative Interpretive Center and taking in the view of the nature preserve from the observation deck, take a leisurely half mile stroll on the paved ADA accessible trail.

Families with very young children will especially enjoy this fairly level and very easy trail.

For those who have more time, plan 2 to 3 hours to explore the interpretive trail system leading deeper into the preserve, about a 2.75 miles roundtrip.  Some of the rugged footpaths are sometimes difficult to find, but in spring and early summer, this is where the gorgeous wildflowers are.

Wildflowers & other Flora

Visitors return in spring year after year to photograph the colorful splendor of this prairie.  The show-stopping array of wildflowers is breathtaking . . . stately Trilliums, brilliant white and bright blue Camas, delicate Lupine, purple Violets, and pretty Shooting Stars give way to early summer blooms of golden Western Buttercups, Chocolate Lilies, Lomatium (wild parsley) and the rare yellow Paintbrush.

Wild strawberries dangle above the ground sheltered by Knickknick and Serviceberry.  Here and there green-grey puffs of Reindeer Lichen add interest to the landscape.

Some Ground-dwelling Lichens from Mima Prairie PDF download

Wildlife & other Fauna

Beautiful butterflies flutter from blossom to blossom; eighteen species have been documented here.

The Mima Mounds natural area is a buggy place.  If you plan to picnic here bring citronella candles to ward off the marauding yellow jacket wasps on warm summer days and bring a strong mosquito repellent, too.  If you are allergic to bee stings, come prepared as the place is buzzing with many bee species.

So many insects make a smörgåsbord for the five kinds of Swallows residing in the preserve, a sort of birders paradise.  This is the only place I’ve ever spotted Cedar Waxwings.

Red-winged Blackbirds are plentiful, as are Meadowlarks.  Western Bluebirds and Yellow Warblers have been spotted in the preserve, too.

Children delight in seeing an occasional salamander or garter snake wriggle through the grasses.  If you visit at the fringes of the day you might be able to photograph deer as they browse through.

American Bird Conservancy

Ground Beetles in Three Western Washington Prairies and Associated Oak Forests PDF download

Mima Mounds Natural Area Preserve Butter Fly Guide PDF download


For over twenty years, Prairie Appreciation Day is celebrated annually on the second Saturday in May.  The Mima Mounds Nature Area Preserve comes alive with ADA accessible activities, nature walks and Native American presentations.

Prairie Appreciation Day Activity Trail Map

Prairie Appreciation Day Self Guided Trail Map

Though we may never solve the mystery of Mima Mounds, we can be grateful for the efforts to preserve their natural history by enjoying the prairie surrounds and the wild things that live there.


South Puget Sound Prairies

Washington State Natural Areas Brochure PDF download


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