There a several sections of tallgrass prairie in Effigy Mounds National Monument and the predominate grass species are Indian grass, big bluestem, switchgrass, and little bluestem. Also found in the prairie are compass plants, butterfly weeds, blazing stars, and purple and yellow coneflowers which add color to the open grasslands. The prairie plants reach their full height in late summer when the grasses mature and blazing star, goldenrods and asters begin to bloom.
Little of the original oak savanna landscape was left when the monument was established in 1949. Small remnants of prairie vegetation, called goat prairies, remained on south facing slopes. These areas were too rocky to plow and too steep to graze cattle. According to early settlers, only a goat would be sure footed enough to keep from falling off the steep slopes. These goat prairies are really remnants of a complex plant community consisting of prairie grasses and wildflowers with an occasional, open grown oak tree.