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The Driftless Area, also known as Bluff Country and the Paleozoic Plateau, is a topographic and cultural region in the Midwestern United States [1] that comprises southwestern Wisconsin, southeastern Minnesota, northeastern Iowa, and the extreme northwestern corner of Illinois. The Driftless Area is a USDA Level III Ecoregion: Ecoregion 52.
The region is within the Driftless Area, a region noted for its karst topography, which includes caves and sinkholes. Tyson's cave is a solutional cave privately owned by the Minnesota Cave Preserve. It is known for the extinct ice-age bones found scattered throughout the cave rooms.
The Effigy Mounds National Monument is noted for being in the Driftless Area, an area of North America which escaped glaciation during the last ice age. The adjacent Driftless Area National Wildlife Refuge takes its name from this region. The Park Service writes:
Much of the area was covered by glaciers about 500,000 years ago, while parts of the Driftless Area were unglaciated. The algific talus slope habitat that harbors the snail is a landscape cooled by air and water emerging from masses of subterranean ice. The ground temperature rarely exceeds 10 °C (50 °F), even in summer.
There are few areas in which the earlier drifts from the glacial deposits of the Pre-Ilionian or Illinoian stages are exposed at the surface. [1] The extreme southeastern and southwestern portions of Minnesota (Driftless Area) have extensive areas of pre-Wisconsin drifts, but they are masked almost everywhere by surficial covering of loess (wind-blown silt).
Ice caves are one characteristic of karst topography, along with sinkholes and cave systems, all of which are present in the area, a portion of the Driftless Area of Iowa. From autumn and into early winter the cave is dry. Ice begins to form in January or February near the entrance and continues down to the lower levels.
The park is in the Driftless Area of Wisconsin, a portion of territory that remained ice free during the last ice age, while land to the east and west was crushed by glaciers. The high bluffs along the Mississippi River and the large deep canyon of the Wisconsin River are evidence of glacial meltwaters reshaping this region.
The air is cooled and vented on the algific slope. In winter, the airflow is reversed. Cool or cold air is drawn through the algific talus into the ice cave, with flowing water or atmospheric humidity being turned to ice. The air temperature on these slopes ranges from "30 degrees F to 55 degrees F spring to fall". [4]