text: Geography Located in the western parts of the St. Lawrence Lowlands, the park is a sandspit formation that extends  into Lake Erie and is up to  thick. With an area of only , it is Canada's smallest national park. Most of the park (about  or 70% of the park consists of marsh, dominated by cattails and ponds although forested areas make up a significant portion of the park, covering about 21% of the park. This sandspit is dominated by till plains which were formed during the last ice age during the advance and retreat of the Wisconsonian ice on a submerged limestone ridge. As the glacier melted and retreated northward, the Lake Erie basin began to fill with water. The movement of sediments altered the coastline, resulting in the present-day shape of Point Pelee. Subsequently, over the centuries, a thin but rich soil has formed. Mineral soils in the park were mapped as well to rapidly drained Eastport sand, which has insignificant profile development. The marshes began to form about 3,200 years ago, based on carbon dating. This was also the same time when the sands began to deposit, forming the present day barriers. The marsh has a closed drainage system owing to the separation of it by two barriers along the east and west side, which usually prevents the free exchange of water. However, when lake levels are higher, the marsh water levels fluctuate with the lake's water levels. The distinctive triangular shape at the southern tip of Point Pelee is caused by the convergence of these two barriers (this spit or tip is the southernmost point of the Canadian mainland). Middle Island, which is located south of the Point Pelee peninsula has an area of approximately  and is the southernmost point in Canada. Virtually all of Middle Island is forested.