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Mima Mounds
Mima Prairie · Thurston County · Natural Area Preserve established 1976
A Thurston County prairie of unexplained soil hills that DNR set aside in 1976, and that NPS named a National Natural Landmark in 1966.
Washington DNR established Mima Mounds Natural Area Preserve in 1976 to protect rare mima-mound landforms and Puget prairie grasslands. The preserve now covers 756 acres of grassland-covered mounds, forest, and Garry oak woodland and savannah. DNR says it also supports prairie butterflies and birds. In 1966 the National Park Service designated the preserve a National Natural Landmark, one of only 17 such landmarks in Washington.
DNR’s Washington Geological Survey guide describes the mounds as irregularly spaced hills of silt, sand, and pebbles. Many are a few feet tall and tens of feet wide. The preserve near Littlerock is one of the best places to see them. Features DNR protects here include Roemer’s fescue–white-topped aster grassland and mima-mound topography. The site has been a research station for more than 50 years, including studies of mound formation and prairie restoration.
This pin is Mima Prairie. The sources below are Washington Department of Natural Resources pages. DNR notes interpretive signs about mound hypotheses; this card does not pick a cause.
- Geography & Geology
- Wildlife & Ecology
- Science / Strange Washington
Sources (3)
government · Tier S
Washington Geological Survey, Department of Natural ResourcesA Guide to the Mima Mounds
government · Tier S
Washington Department of Natural ResourcesMima Mounds Natural Area Preserve
government · Tier S
U.S. Geological SurveyMima Prairie (GNIS 1511617)
Last reviewed: September 21, 2026
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