Southeastern Minnesota’s landscape was shaped by four glacial periods over the past 2 million years, with masses of moving ice and snow covering the state at various times and the last glacier, the Wisconsin, melting away about 10,000 years ago. This corner of the state is part of the driftless area, which was not covered by the last glacier, and possibly in its extreme southeastern corner was never glaciated at all. As the land descends into the Mississippi River valley, there are no natural lakes, and deep valleys and towering bluffs reflect erosion caused by glacier meltwaters to the north and west. Roadcuts and bluffs expose limestone, sandstone, and dolomite deposited by oceans that covered the area several times, most recently about 70 million years ago. Because these stones erode easily through groundwater, the area contains numerous sinkholes and caves, including Fillmore County’s Niagara and Mystery caves. Rich soil and natural beauty drew early settlers and later tourists, and numerous trails now allow residents and visitors to explore the area’s geology.