 Sarnia is located on the eastern shore of Lake Huron at its extreme southern point where it flows into the St. Clair River . Most of the surrounding area is flat , and the elevation ranges from 169 metres ( <unk> ft ) and 281 metres ( 922 ft ) above sea level . The soil mostly comprises clay . Despite this high percentage of clay , the soil is remarkably rich for cultivation . Prior to the Ice Age , glaciers covered most of the area , as can be seen not only by the existence of the Great Lakes themselves but also of alluvial sand deposits , terminal moraines , and rich oil reserves . The entire area was submerged and plant and animal matter formed many layers of sediment as they settled after the waters <unk> . Sarnia is not part of the Canadian Shield and is located just beyond its southernmost reaches , 290 kilometres ( 180 mi ) West of Toronto and 106 kilometres ( 66 mi ) North of Detroit . 
