is characterized by glaciation. Most of the park lies on red clay sediments deposited 10,000 years ago at the bottom of a proglacial lake. Ice sheets covered Minnesota as many as twenty times over the 2 million years of the Quaternary glaciation, each advance largely obliterating the results of the previous. Nearly all of Minnesota's glacial landforms derive from the last of them, the Wisconsin glaciation. One feature of this time in the park are the rock ridges near the campground, scoured smooth by the glacier and known as roches moutonnées. Another is the Thomson Moraine, a ridge along the northwest boundary. This terminal moraine comprises rock and debris dropped at the farthest reach of the Laurentide Ice Sheet's Superior Lobe. As the climate warmed at the end of the Pleistocene epoch, the Superior Lobe shrank northeastward. The deep basin gouged by the ice filled with meltwater around 12,000 years ago as Lake Duluth. Since the eastern shore was formed by the towering wall of the ice sheet, the lake was higher than modern Lake Superior. The St. Louis River, flowing into Lake Duluth, dropped its sediment load onto the lakebed, forming layers of silt and sand alternating with clay. The clay layers include incongruous cobbles and boulders, dropstones which melted free from icebergs floating above. As the Laurentide Ice Sheet receded further, lower elevation outlets were exposed and the lake level dropped significantly. The St. Louis River flowed across the now-exposed lakebed, etching wide and changeable meanders into the soft sediments. On the south side of the river are several steep, curving valleys that are former meanders. Slumping of the unstable clay walls further widened the main valley. The river's downcutting eventually passed through the Pleistocene lake sediments and into the Precambrian bedrock, exposing the rocky, gorge that characterizes the western half of the park. Wildlife The park is inhabited by 46 species of mammals and is an important wintering area for White-tailed Deer. Black Bears, Wolf packs, and Coyotes have been spotted within the park. The park houses 173 species of birds including the Pileated Woodpecker, Northern Harrier, and the Great Blue Heron. Sixteen species of (non-venomous) reptiles are found within the park. Recreation The park has over 50 miles of hiking trails, with several scenic overlooks over the Saint Louis River. Certain trails, such as the Greely Creek Trail, Triangle Trail, and Gill Creek Trail, are also