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Rainier Visitor Guide.com Information Resource Center
"Mounds of Mystery..... ? ? ? "
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Mima Mounds: Below the western slopes of Mount Rainier the topography changes to a native
grassland ecosystem - the "Puget Prairie".   The early summer prairie wildflower displays with acres of purple
camas flowers are a wonderful sight and the summer butterfly displays can be fantastic - but it is the "Mounds of
Mystery" that the prairie is famous for.

    The bizarre prairie is full of thousands of strange and
    wondrous "Mounds of Mystery" or Mima Mounds - soil and
    gravel mounds that are closely-packed, some 6-8 feet high
    and about 30 feet across.   The "pimpled prairies" cover
    about 10,000 acres and include tracts on Fort Lewis and near
    Yelm, Roy and Spanaway.   The best location to view the
    mounds is the Mima Prairie near Little Rock, close to exit 95
    off I-5.  Due to its unique topography, this 624 acre site was
    designated a National Natural Landmark in 1968 by the
    National Park Service and is the nation's best example of the
    unusual "mima mound" phenomena.  Visitor facilities include
    a 1/2 mile paved interpretive trail, an interpretive shelter with
    displays, a two mile loop trail, parking lot and restroom.



     
Mima Mounds National Landmark

Many hypotheses have been proposed about the origin of the mysterious, regularly spaced six to eight foot tall
mounds.   Before farmers began leveling them, they stretched for more than 20 miles.  More than 30 theories
exist as to the origin of these "Mounds of Mystery - many of which contain over 100 tons of soil - and there are
thousands of them.  The most popular theories attribute the mounds to pocket gophers working over 6000 years
while others blame the phenomena on seismic activity, tsunamis, glaciers, permafrost, and even ufo's - which
have a history of sightings near Mount Rainier.   The seismic theory is based around the phenomena that if you
tap on a sheet covered with sand the sand will clump together into small dimples - looking like "mini" mounds.  

    Recent ground-height laser measurement
    studies have garnered support for the glacier
    meltdown theory which suggests that the glaciers
    that covered the area were full of depressions as
    the sun melted them and the melted glacier
    water repeatedly washed gravel and soil into
    these depressions as the water burst out of ice
    dams which would be occurring throughout the
    melting glacier.  Like the gopher, seismic, and
    other theories, it sounds somewhat far-fetched
    when you actually see the mounds.  It appears
    the mounds may always remain a mystery !

    What made these Mounds of
    Mystery ?

  • Gophers ?
  • Glaciers ?
  • Earthquakes ?
  • Volcanoes ?
  • Aliens ?
  • Tsunamis ?
  • Ancient Fish Nests ?
  • Wind Erosion ?
  • Steam Vents ?




    Photo Credit: Chris Joseph Taylor / The Seattle Times

See the Famous Mima Mounds just 5
minutes off I-5 at exit 95 on the way to
Mount Rainier National Park.



Perhaps Mount Rainier was the culprit ?  
When volcanoes erupt they commonly deposit large pieces of debris throughout the ash or mud flow.   Many
times large chunks of ice and glacier pieces are carried along with the debris only to later melt leaving large
depressions in the debris flow landscape.  These debris pieces and ice chunks form hills and holes that make up
the unusual landscape below volcanoes which is technically referred to as "Hummocks".  Could the mima
mounds be the hummocks of Mount Rainier eroded over time ?  Hike the
Hummocks Trail at Mount St.
Helens for a first hand look at this phenomena.



    Mount Shasta Hummocks









    Bezymianny Volcano Hummocks












    Augustine Volcano Hummocks









Mima Mound Mystery Solved ?  Remember - you heard it here first !

Or was it...really the work of moles and gophers.....?

    During the course of the soil surveys of eastern Stanislaus and Merced Counties of California, where
    similar mounding geography ( microrelief) is widespread, the phenomenon was studied over a
    period of eight years.  The results were published in the Soil Science Society of America Journal.  All
    known theories were evaluated and compared with the evidence which could be observed in the
    field. The evidence studied included the nature of the mounds such as shape, size, internal structure,
    distribution of gravel, the burrows of ants and rodents; the distribution of the microrelief with respect
    to soil types and the pattern of occurrence of mounds under various conditions.

    The theories of origin which were tested included erosional theories based on wind action and water
    action, fluviatile, submarine and sub-lacustrine currents; eruptional theories suggesting gas-vents,
    sand boils and hydrostatic pressure; and biological theories based upon the activity of ants, ground
    squirrels and pocket gophers.
It was concluded that the evidence points clearly to a biological explanation, and that the pocket gopher is responsible for Mima
mound microrelief.
 

This study was complete in 1954.   However a number of studies since disagree with this finding.  55
years later scientists still debate the cause of these Mounds of Mystery.


source: Rainier Visitor Guide.com
Mima Mounds - SW Washington
Mounds of Mystery - Mima Mounds
Mount Shasta Hummocks
Bezymianny (Russia) Hummocks
Augustine (Alaska) Hummocks