Marker Logo HMdb.org THE HISTORICAL
MARKER DATABASE
“Bite-Size Bits of Local, National, and Global History”
“Bite-Size Bits of Local, National, and Global History”
Near Littlerock in Thurston County, Washington — The American West (Northwest)
 

What We Know for Sure

 
 
What We Know for Sure Marker image. Click for full size.
By Duane Hall, September 1, 2010
1. What We Know for Sure Marker
Inscription. The Mima Mounds were formed some time after ice age glaciers began receding 16,500 years ago. Their origin has puzzled scientists and curious visitors since the mid-1800s. Research has revealed what we know so far about the glacial history of this area and the structure and pattern of the mounds.

Evidence of Ice Ages Beneath the Mounds

About 2.2 million years ago as earth’s climate cooled, massive ice sheets formed far to the north. These glaciers advanced southward and melted northward many times. Thousands of feet thick, they gouged underlying land and picked up immense loads of gravel and rock.

The last advance of ice into western Washington ended about 16,500 years ago. Mima Prairie is at the edge of its southernmost reach.

As the glaciers retreated, torrents of meltwater fanned across the landscape and deposited a load of gravel and rock. This gravelly outwash became the well-drained, dry soils of today’s prairies.

What is a Mima Mound?

Mounded landscapes are found in several areas of North America and in a variety of habitats. They are called pimple mounds near the Gulf of Mexico, prairie mounds in the northern Great Plains, and hogwallow mounds in California. Mounds in each location may have a unique origin.

In South Puget Sounds, Mima Mounds
Mima Mounds and the Glacial Age image. Click for full size.
By Duane Hall, September 1, 2010
2. Mima Mounds and the Glacial Age
Close-up of graphic on marker
are located only on top of layered sediment deposited by glacial meltwater.

They appear to be restricted to a single terrace level along the Deschutes River south of Olympia. Mounds are circular or elliptical 8 to 10 mounds per acre. Mounds are usually about the same size and shape in any one area, but some very lot mounds are found among larger mounds.
 
Erected by Washington State Department of Natural Resources.
 
Location. 46° 54.271′ N, 123° 2.918′ W. Marker is near Littlerock, Washington, in Thurston County. Marker can be reached from Waddell Creek Road SW 0.4 miles south of Deer Tail Road SW. Click for map. Marker is located in Mima Mounds Natural Area Preserve in a kiosk that is a short walk from the parking lot; the above directions are to the intersection of Waddell Creek Road SW and the driveway to the Mima Mounds parking lot. Marker is in this post office area: Littlerock WA 98556, United States of America.
 
Other nearby markers. At least 8 other markers are within 12 miles of this marker, measured as the crow flies. Mima Mounds: The Mysterious Work of Nature (here, next to this marker); Scientists Still Search for an Answer (here, next to this marker); Mima Mounds: A Special Prairie (here, next to this marker); Ecological Connections
A Mima Mound image. Click for full size.
By Duane Hall, September 1, 2010
3. A Mima Mound
Close-up of image on marker
(here, next to this marker); The Lone Tree (approx. 11.1 miles away); The Medal of Honor Monument (approx. 11.4 miles away); POW AND MIA Monument (approx. 11.4 miles away); Marking the End of the Oregon Trail 1844 (approx. 11.8 miles away). Click for a list of all markers in Littlerock.
 
Also see . . .  Mima Mounds: Mystery hides in vast prairie. Newspaper article from the July 6, 2008 edition of the Seattle Times. (Submitted on February 16, 2014.) 
 
Categories. Natural Features
 
Similar Mounded Areas in North America image. Click for full size.
By Duane Hall, September 1, 2010
4. Similar Mounded Areas in North America
Close-up of map on marker
Mima Mounds image. Click for full size.
By Duane Hall, September 1, 2010
5. Mima Mounds
Mima Mounds image. Click for full size.
By Duane Hall, September 1, 2010
6. Mima Mounds
 
 
Credits. This page originally submitted on , by Duane Hall of Abilene, Texas. This page has been viewed 250 times since then and 13 times this year. Photos:   1, 2, 3, 4. submitted on , by Duane Hall of Abilene, Texas.   5, 6. submitted on , by Duane Hall of Abilene, Texas. This page was last revised on June 16, 2016.
 
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