- 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.
- The mounds were formed approximately 15,000 years around the time of the last glacial retreat.
- The volcanic rock, andesite, is heavily present in the mounds.
- 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.
- Indigenous people used controlled burns at the site [Mime Prarie] to maintain the landscape as a prairie, allowing vegetation used for food or medicine to prosper.
- The mounds, also described as hillocks, are situated on a plain of underlying cobble that is most likely a remnant of a glacial lake.
- 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.
- The origins of the word, mima (MY-ma), has been reported to be unknown, though it may mean, “newness”, under the language of the Chehalis people.
- The site [Mima Mounds NRCA] is located on an outwash plain of the Vashon Glacier.
- 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.
- Immediately north of Mima Mounds was the southern reach of the Puget Lobe.
- 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).