Radiocarbon dates of 18 300 ± 380 years BP (GSC-2668) and 18 400 ± 1090 years BP (GSC-2670) on moss fragments from the clay near the base of a core from Chalmers Bog, Alberta indicate that the classical Wisconsinan "Ice-free Corridor" was in existence in the foothills of southern Alberta by this time. Palynological studies show sparse, herbaceous, tundra-like vegetation probably prevailed at this time in the area surrounding the small lake formed in the abandoned glacial spillway. Later, shrubs became more prominent to form a shrub tundra environment. Sometime before 8220 years BP (GSC-2851) trees began to invade the area and the Pinus contorta dominated coniferous forest extant in the area today began to form. Bog and fen vegetation invaded the shallow lake basin about this time as well to form the bog that occupies the basin to the present day.