Located on an extensive outwash sand terrace along the Wisconsin River, Avoca Prairie and Savanna contains the largest natural tallgrass prairie east of the Mississippi River. Frequent flooding has created braided stream topography characterized by low, sandy ridges interspersed with small linear wetlands giving a local relief of 4 feet. The moist prairie and wetland swales contain more than 200 species of vascular plants including large numbers of rattlesnake master, Michigan lily, prairie blazing-star, and two rare species – tall nut-rush (Scleria triglomerata) and prairie Indian plantain (Arnoglossum plantagineum). Big blue-stem, prairie cord grass, Indian grass, and sedges dominate the wet areas while little blue-stem, prairie drop-seed, and June grass are common on the drier ridges. Permanent and ephemeral swales contain aquatic species such as sweet-flag, yellow water buttercup, and common bur-reed. Some of the showy species include sweet grass, white wild indigo, flowering spurge, prairie smoke, bottle gentian, cardinal flower, and swamp candles. Oak openings, with large open-grown black and bur oaks, are an outstanding feature of this natural area looking much as they did during the original land survey of 1833. Even today, from many points on the prairie, the same presettlement character has been preserved, with completely natural vistas still accessible in all directions. Avoca is also home to rare animals including red-shouldered hawk (Buteo lineatus), northern harrier (Circus cyaneus), short-eared owl (Asio flammeus), and Blanding’s turtle (Emydoidea blandingii). Avoca Prairie and Savanna is owned by the DNR and was designated a State Natural Area in 1968.