Mima Mounds National Natural Landmark, Washington
N 46° 54.271 W 123° 02.919
10T E 496294 N 5194554
Quick Description: The Mima Mounds were designated a National Natural Landmark in May 1966. There is a self-guided walk with free maps, an impressive interpretive display and educational plaques along a paved path.
Location: Washington, United States
Date Posted: 8/2/2009 2:23:51 PM
Waymark Code: WM6XKY
Views: 2
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IN BRIEF
One and one-half miles west of Little Rock in Thurston County.
Prairie containing unusual soil pimples of black silt-gravel
ranging in height from barely perceptible to a maximum of seven
feet. Owner: State
DESIGNATION DATE
May 1966
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Mima Mounds Natural Area Preserve. Mima Mounds NAP west of
Littlerock is a 445 ac preserve established in 1975 to preserve an
undisturbed example of mounded prairie and the rare Roemer’s
fescue/white-topped aster community (DNR 1997).
Mima mounds. Mima mounds are a distinctive feature of some south
Puget Sound prairies. These low, regular, rounded mounds average
perhaps 6-8 feet in height and 35-50 ft in diameter, and have a
density of about 8-10/ac (Washburn 1988, Kruckberg 1991). The
mounds contain a bi-convex lens of fine dark soil with a high
organic matter content (Mielke 1977). The mounds occur where a
layer of fine loose
material exists over a harder layer of rock or compacted clay or
gravel. Similar mounds, which may or may not be of similar origin,
occur on other grasslands in various locations in North America and
on other continents. The origins of these mounds have been debated
for over 100 years.
(pg 23) Dalquest and Scheffer (1942) first hypothesized that the
activity of pocket gophers was the force responsible for the
creation of Mima mounds. Basically, gophers push material toward
the center of the mound as they dig outward in their territory
which is located in the same place year after year (Cox and Allen
1987, Cox and Hunt 1990). Other hypotheses include various geologic
and geofluvial processes (Washburn 1988, Berg 1989). Mima mounds
co-occur with burrowing rodents in North America, South America,
and Africa; Reichman and Seabloom (2002) consider the burrowing
mammal hypothesis for their formation to be the simplest
explanation. The gopher hypothesis has been accepted by many
ecologists, but no convincing evidence has been found for it, or
any other hypothesis, to be widely
accepted.