Reconnaissance from a light aircraft has revealed areas of polygonal ground east of Kitchener, Ontario. Examination of aerial photographs of the same region has shown additional polygons all developed upon Port Stanley II Till. Trenching of a polygon has exposed wedge-shaped sand and gravel infilled structures interpreted as ice-wedge casts. The wedges are believed to have been active prior to 13 000 years B.P., probably under tundra conditions, with mean annual air temperatures some 25 °F (13–14 °C) cooler than present.