Dalles of the St Croix

The Dalles of the St. Croix River State Natural Area is an L-shaped segment of the St. Croix River gorge cut in Precambrian basalt. The main gorge, 100 feet deep, is of post-glacial origin, cut by running water during glacial lake drainage. The site is well-known for its cylindrical potholes, which were formed by the grinding action of sand and small stones swirling in strong currents. The potholes are smaller than those on the Minnesota side but are still spectacular, some as large as 6 feet w ide and 12 feet deep. Most exposures are barren, but sites with more moisture contain polypody fern, fragile fern, rusty woodsia, fragrant fern, mosses, and lichens. Areas of sparse dry forest of red cedar, basswood, white pine, and bur, white, and black oaks occur throughout the site. Big bluestem, blueberry, sumac, long-leaved bluets, bearberry, and poverty oat grass are characteristic plants of the rocky area.