| Summary: | The UW-Madison Arboretum represents a landscape significantly altered by the Late Wisconsinan Glaciation (~25,000-10,000 BP). Soil and bedrock cores from wells along with observed glacial features were examined to determine the pre-glacial landscape of the arboretum and the effects that multiple glaciations had on that landscape. Prior to the Pleistocene, the north part of the arboretum was a deep river valley incised into Ordovician and Cambrian bedrock surrounded by bluffs. The Pre-Illinoisan and Illinoisan glaciations, though likely reaching the arboretum, have left few permanent effects because the Late Wisconsinan Glaciation obscured signs of earlier glacial advances and retreats. About 25,000 BP, the Green Bay Lobe of the Laurentide Ice Sheet advanced southwest from Canada to cover south central Wisconsin. After a standstill of 1000-5000 years, the Green Bay Lobe retreated from the arboretum, leaving glacial features including a drumlin, two recessional moraines, a kettle, and materials including glacial erratics and unstratified drift. Outwash from the retreating glacier filled moraine-dammed lowlands in the Madison area, forming glacial lakes including Yahara, Curtis, and Greene. In the last 10,000 years, the levels of these lakes have slowly lowered as the Yahara River incises into its bed, and glacial lakes Curtis and Greene have long since filled in, while part of Yahara remains as Lake Wingra. Two of Glacial Lake Yahara's abandoned shorelines are visible in the arboretum, though they have not been dated. In the time since the arrival of humans in Wisconsin, and particularly since European settlement in the 19th century, features of the arboretum's post-glacial landscape have been altered by human actions such as gravel mining, sandstone quarrying, farming, and the damming of Wingra Creek.
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