What is a mima mound? These huge bumps in the ground look like either an ancient burial site, an acne covered face, a secret braille text just for UFOs, or perhaps a giant connect-the-dot game for Bigfoot. These fascinating polka-dot mounds are a geologic phenomenon and can be found near Chehalis, Washington.
Are they formed by blowing sediment? Seismic shaking? Waterlogged soil? Although they can be found in other parts of North America, an explanation on how they were formed has not been found that explains whether all mounds are derived from the same cause. Examination of the Mima Mounds has shown they are not all made of the same soil type, further complicating finding a definitive solution to their origin.
The word “Mima” is derived from a Native American language meaning “A little further along” or “downstream” and the local mounds were named after the Mima Prairie in Thurston County. Other areas where similar mounds are found are called “Prairie Mounds.”
The site is not widely known but visitors are welcome. It is part of the Mima Mounds Natural Area Preserve, a protected natural area of over 600 acres that includes the Mima Mounds, grasslands, wildflowers, and woodland. There is an interpretive center to help you understand what you see, walking paths that include a ½ mile loop that is ADA accessible, and two longer gravel paths. Remember your camera to capture this unusual landscape!
Open April-September 8:30 am – 8:30 pm and Oct – March 8:30 – 5:30 pm. A Washington State Discover Pass is required to park at the site.
Not far off of I-5, this is a great stop for those driving between Portland and Seattle as a mid-way break to stretch your legs.
From southbound or northbound Interstate 5, take Exit 95 and turn west on Highway 121 (Maytown Road SW) toward Littlerock. In Littlerock, continue west (forward past the school, past the intersection with Littlerock Road that curves south, and past the mini mart/gas station on the right) onto 128th Avenue. Travel about 0.8 mile where 128th Avenue ends at a ‘T.’ on top of the hill. Turn right onto Waddell Creek Road and travel about 1 mile. The entrance to Mima Mounds Natural Area Preserve will be on the left.