This area of expansive prairie-covered mounds south of Tumwater is a scientific curiosity. Theories on the creators of these abundant earthen mounds range from gophers to glaciers. Many scientists believe they may have been created by freezing and thawing conditions when the last ice age glaciers retreated from the area some 10,000 to 15,000 years ago. The paved Mima Mounds Natural Trail (.5mi) leads through the mounds; a 2mi loop extends south. The mounds support a native prairie grassland which includes wildflowers, butterflies and birds.