Mima Mounds Natural Area Preserve

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Mima Mounds Natural Area Preserve
Mima Mounds Natural Area Preserve in Thurston County, Washington 01.jpg
Mima mounds in May 2023
Mima Mounds Natural Area Preserve
Mima Mounds Natural Area Preserve
Mima Mounds Natural Area Preserve
Interactive map of Preserve location
LocationSouthwest corner of Thurston County, Washington, United States
Nearest town Littlerock, Washington
Coordinates 46°53′N123°03′W / 46.89°N 123.05°W / 46.89; -123.05
Area756 acres (306 ha)
Designation National Natural Landmark
Established1976 [1]
Governing body Washington Department of Natural Resources
Website Department of Natural Resources - Mima Mounds

Mima Mounds Natural Area Preserve is a state-protected Natural Area in the southwest corner of Thurston County, Washington. The site was designated as a National Natural Landmark in 1966 as an example to protect mima mounds.

Contents

History

The mounds were formed approximately 15,000 years around the time of the last glacial retreat. Indigenous people used controlled burns at the site to maintain the landscape as a prairie, allowing vegetation used for food or medicine to prosper. [2] The origins of the word, mima (MY-ma), has been reported to be unknown [2] , though it may mean, "newness", under the language of the Chehalis people. [3]

The mounds were documented by Charles Wilkes in May 1841 during a global expedition. Wilkes speculated the mounds were burial sites of Native Americans, but after digging into a few of the features, no relics were found by his team. The Wilkes research of Mima Mounds is the first known scientific attempt at the preserve. [3] [4]

In 1966, the mounds were designated a National Natural Landmark and the area was established as the Mima Mounds Natural Area Preserve in 1976. [1]

Formation theories

The formations have been suspected to be burial mounds of indigenous people, piles created by either floods or glaciers, or remnants of where trees once stood after a forest was devasted by a tornado. The Chehalis tribe has a history of stories mentioning that the mounds are from the remains of large sea mammals, coming to rest after being washed away during a large flood. A more common theory, which emerged in the 1940s, states that the mounds were formed by burrowing animals, most likely gophers. In the 1990s, another hypothesis suggested the landscape was formed by earthquakes. As of 2025, no consensus has been reached in the scientific community on how the mounds were formed. [3]

Geography and geology

The mounds were once part of a larger stretch of a prairie ecosystem encompassing approximately 180,000 acres (73,000 ha), spanning from present-day Joint Base Lewis–McChord through Chehalis and into Oakville. The preserve is located between Capitol State Forest and the community of Littlerock. [2] The preserve is listed as either over 600 acres (240 ha) [3] or precisely at 756 acres (306 ha). [1]

The site is located on an outwash plain of the Vashon Glacier.[ citation needed ] Immediately north of Mima Mounds was the southern reach of the Puget Lobe. [3]

The mounds, also described as hillocks, are situated on a plain of underlying cobble that is most likely a remnant of a glacial lake. The volcanic rock, andesite, is heavily present in the mounds. The rock traveled from Mount Rainier during extensive flooding in the region when the Glacial Lake Carbon ice dam failed,. Gravel, sand, and silt account for the remaining components of the features. [3]

Features

There are approximately 8-10 mounds per acre, measuring 1–7 feet (0.30–2.13 m) in height and having diameters 7–40 feet (2.1–12.2 m). [5] [6] [3] Spaced relatively evenly, vegetative growth on the mounds include grass, moss, and wildflowers. A few of the hillocks contain trees. [3]

Ecology and environment

The landscape contains natural vegetation such as camas lilies, huckleberry, Indian plum, and salal. The mounds are usually covered in various shades of lichen and moss. Gophers have been native to the area since the glaciers retreated. [2] The site contains 756 acres (306 ha) of Garry oak woodland, oak savanna, and prairie grasslands. [1]

Golden paintbrush, once common on the prairie and at the preserve, is considered a threatened species. Invasive plants include Douglas fir and Scotch broom. [2]

Butterflies

The preserve is host to wildflowers and many species of butterfly (some endangered), with activity between spring and early fall, mid-morning and mid-afternoon. [7]

Recreation

A short, ADA-accessible 0.5 mile paved trail leads to a small interpretive shelter and observation deck with view of the prairie. [6] A longer, unpaved gravel 1.5 mile loop trail to the south explores the mounds with possible views of Mount Rainier and Mount St. Helens. [10] [11]

See also

References

  1. 1 2 3 4 "Mima Mounds Natural Area Preserve". Washington State Department of Natural Resources . Retrieved June 16, 2025.
  2. 1 2 3 4 5 Seven, Richard (July 6, 2008). "Mima mounds: Mystery hides in vast prairie". The Seattle Times . Retrieved July 22, 2025– via seattletimes.com.
  3. 1 2 3 4 5 6 7 8 Berger, Knute (October 10, 2025). "Mossback's Northwest: The mystery of Washington's Mima Mounds". Cascade PBS . Retrieved January 27, 2026.
  4. ↑ "Mima mounds: The mysterious work of nature". Historical Marker Database (historical marker). Retrieved June 16, 2025.
  5. ↑ Kresge, Joanna (July 17, 2024). "Investigating the mysterious Mima Mounds". South Sound Magazine. Tacoma, WA. Retrieved June 16, 2025– via SouthSoundMag.com.
  6. 1 2 Emma (January 16, 2023). "Washington's mysterious Mima Mounds". Adventures. Pines and Vines (blog). Portland, OR. Retrieved June 16, 2025– via pinesnvines.com.
  7. ↑ "Butterfly guide" (PDF). Mima Mounds Natural Area Preserve. Olympia, WA: Washington Department of Natural Resources . Retrieved June 16, 2025– via dnr.wa.gov.
  8. ↑ "Taylor's checkerspot (Euphydryas editha taylori)". Species habitats. Olympia, WA: Washington Department of Fish & Wildlife . Retrieved June 16, 2025– via wdfw.wa.gov.
  9. ↑ "Mardon skipper (Polites mardon)". Species habitats. Olympia, WA: Washington Department of Fish & Wildlife . Retrieved June 16, 2025– via wdfw.wa.gov.
  10. ↑ "Mima Mounds". Washington Trails Association . Retrieved June 16, 2025.
  11. ↑ "Mima Mounds Natural Area Preserve". Experience Olympia. Retrieved June 16, 2025.
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