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Mysterious Mima Mounds: Wildflowers and Geology in Thurston County

Published on: May 01, 2008

Spring is the perfect time to go to the 600-plus-acre Mima Mounds Natural Area Preserve near Olympia. A leisurely stroll along the paved path through the preserve is an easy one for little ones. Pick up a guide at the entrance to help identify wildflowers, butterflies and small creatures thriving on this endangered prairie land. Rare butterflies, such as the endangered Mardon skipper and the reintroduced Taylor’s checkerspot, can be spotted flitting among the wildflowers. They are active in May.

No one is sure of how the Mima Mounds were formed. These “mounds” are piles of dirt about 6 feet tall and spaced somewhat regularly 20 to 30 feet apart. There are three predominant theories about their formation. The first is based on the premise of glacial activity, suggesting that glaciers left sediment (dirt, rocks, silt) as they melted 12,000–15,000 years ago. Over time, erosion formed the mounds. Another theory is that seismic activity from earthquakes thousands of years ago formed the mounds. A third theory is that 15,000 years ago the pocket gopher, which builds mounds up instead of down in rocky soil, created the mounds! Whatever the cause, the mounds are fascinating to see. Climb the tower near the preserve’s entrance to get a good impression of the rolling prairies.

The prairie ecosystem in the south Puget Sound region is in peril from residential and agricultural development, invasion of non-native plants and the encroachment of forestland. There is a loss of birds and animals that are dependent on the habitat. One hundred years ago, more than 150,000 acres of south Puget Sound was prairie; now less than 3,000 acres remain. This geological wonder is part of a restored prairie.

The Nature Conservancy is working with other nonprofit groups, Washington state and the federal government to restore and maintain this threatened habitat. According to Carrie Marschner, a prairie land steward with The Nature Conservancy, the prairie area is a critically endangered habitat. Restoration efforts such as planting native grasses and wildflowers are combined with removing invasive plants such as Scotch broom.

Springtime on the prairie is known for its wildflowers, such as the blue camas, chocolate lily, golden Indian paintbrush, bluebells and violets. Some wildflowers, like the golden Indian paintbrush, are rare. Found mainly in western Washington, primarily in the prairie areas of Thurston County, it is the only yellow paintbrush you will see.

Before white settlers came to the area, Native Americans used to burn the fields in the fall to encourage the spring growth of the blue camas bulbs, a plant favored by many tribes as an important food staple. Harvested in late summer, the bulbs would be roasted in a pit oven for a couple of days and eaten much like sweet potatoes, or cooked and then dried in the sun in preparation for winter eating. Sometimes the dried camas was ground into meal to make a cereal. The fields were tended to ensure that the bulbs would be large for harvest. After harvest, the replanting of small bulbs took place for the next year. Women were the caretakers and harvesters of the bulbs.

Any spring day is fine for a visit to the Mima Mounds, but May 3 is special. The 13th Annual Prairie Appreciation Day (cosponsored by The Nature Conservancy, Friends of Puget Prairies, Thurston County Parks and Recreation Department, and Washington State Department of Fish and Wildlife) is a family-friendly event open from 10 a.m. to 3 p.m. You’ll find more than a dozen activities offering fun for all ages, but especially for children. Take a guided wildflower walk; see a collection of small prairie creatures; pull some invasive Scotch broom; make wind wands, camas digging sticks and wildflower seed balls; or hop on a wagon for an old-fashioned hay ride. Glacial Heritage Prairie, a 1,000-acre area owned by Thurston County and normally closed to visitors, is open that day to the public. Bring a picnic to enjoy on the prairie. It is located only about one mile south of Mima Mounds.

Take the family for a fun day on May 3, and then return another day to volunteer for a restoration workday at Glacial Heritage Prairie or Mima Mounds Natural Area Preserve. Volunteers restore native plants to the area, or work to weed the invasive non-native plants. For information, contact The Nature Conservancy at 206-343-4344.

Enjoy an outing where children can see flowers, butterflies, small prairie animals and the unusual hills of dirt known as the Mima Mounds. Bring your binoculars, your camera and your curiosity.

Janice Lovelace, parent of two, is an outdoor enthusiast and avid photographer. A nationally published author, she frequently writes about traveling with children.

If you go . . .

Glacial Heritage Preserve is located a few miles south of Littlerock in Thurston County. Exit I-5 at Littlerock (Exit 95) and drive west straight through Littlerock to the “T” intersection with Waddell Creek Road/Mima Road. Turn left (south) on that road, drive 2.7 miles and turn left onto an unnamed gravel road. Follow the road to parking. Signs will mark the way from Littlerock on Prairie Appreciation Day.

Mima Mounds Natural Area Preserve: Exit I-5 at Littlerock (Exit 95). Drive west through Littlerock and continue on 128th Avenue Southwest until it ends at a “T” intersection with Waddell Creek Road. Turn right on Waddell Creek Road. The Mima Mounds entrance will be on the left. Keep a good lookout — it’s easy to miss! 360-902-1340.

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