- Mima Mounds Natural Area Preserve (NAP) was established in 1976 to protect rare examples of “mima mound” landforms and Puget prairie grasslands. The site includes a small Garry oak woodland and savannah (widely spaced oak trees with grass understory) and also supports a variety of prairie dependent butterflies and birds, and Douglas-fir forest. The NAP currently comprises 756 acres of grassland covered mima mounds, forest and oak woodland. In 1966, the National Park Service designated Mima Mounds Preserve as a National Natural Landmark, for its representation of our nation’s natural landscape; one of only 17 such landmarks in Washington state.