The Dells of the Wisconsin River encompasses over five miles of the Wisconsin River corridor with a spectacular gorge, cliffs, tributary canyons and rock formations carved into Cambrian sandstone. Formed between 510-520 million years ago, some cliffs rise over one hundred feet above the water and have been shaped by the erosive processes of water and wind. With a variety of exposures and moisture regimes, the cliffs afford many different niches for plants, some of which are very rare in Wisconsin. One species is known from only two places on Earth - here and in the Kickapoo Valley, and grows on protected rock ledges. Other rarities are also present. This area contains a mosaic of plant communities including northern and southern oak/pine forests, oak savanna, and moist and dry cliffs. Rare animals include six dragonfly species, six rare mussels and numerous birds.