lobe and Lake Michigan lobes on the east. The northern and eastern lobes were in part diverted around the area by the Watersmeet Dome, an ancient uplifted area of Cambrian rock underlain by basalt in northern Wisconsin and western upper Michigan. The southward movement of the continental glacier was also hindered by the great depths of the Lake Superior basin and the adjacent highlands of the Bayfield Peninsula, Gogebic Range, Porcupine Mountains, Keweenaw Peninsula, and the Huron Mountains along the north rim of the Superior Upland bordering Lake Superior. The Green Bay and Lake Michigan lobes were also partially blocked by the bedrock of the Door Peninsula, which presently separates Green Bay from Lake Michigan. Another factor that may have contributed to the lack of glaciation of the Driftless area is the fractured, permeable bedrock within the Paleozoic Plateau underlying it, which would have promoted below-ground drainage of subglacial water that would otherwise have lubricated the underside of the glacial ice sheet. The dewatering of the underside of the ice sheet would have inhibited forward movement of the glacier into the Driftless Area, especially from the west. In the adjacent glaciated regions, the glacial retreat left behind drift, which buried all former topographical features. Surface water was forced to carve out new stream beds. This process was absent in the Driftless Area, where the original drainage systems persisted during and after the ice age. Water erosion continued carving the existing gullies, ravines, stream beds, and river valleys ever deeper into the paleozoic plateau, following the original drainage patterns. Characteristic landforms Geology Overall, the region is characterized by an eroded plateau, with bedrock overlain by varying thicknesses of loess. Most characteristically, the branching river valleys are deeply dissected. The bluffs lining this reach of the Mississippi River currently climb to nearly . In Minnesota, pre-Illinoian-age till was probably removed by natural means prior to the deposition of loess. The sedimentary rocks of the valley walls date to the Paleozoic Era and are often covered with colluvium or loess. Bedrock, where not directly exposed, is very near the surface and is composed of "primarily Ordovician dolomite, limestone, and sandstone in Minnesota, with Cambrian sandstone, shale, and dolomite exposed along the valley walls of the Mississippi River." In the east, the Baraboo Range, an ancient, profoundly eroded monadnock in south central Wisconsin, consists primarily of Precambrian quartzite and rhyolite. The area has not