The St. Lawrence River is the primary drainage form the entire Great Lakes region. The St. Lawrence Valley Province is a lowlands region along the St. Lawrence River between glacial Lake Ontario and where the river becomes a tidewater estuary near Quebec City (the Gulf of St. Lawrence is one of the largest estuaries in the world)(Figure 47). The valley includes parts of northern New York and parts of southern Ontario and Quebec. The province is flanked on the south by the Adirondack dome and uplands of the southern Canadian Shield to the north. The elevation ranges slopes gently from about 1000 feet in the west to about 80 feet in the east, but consists mostly of gentle rolling hill country. The bedrock consists of sedimentary layers (Ordovician shale and limestone, and Cambrian sandstone) with a veneer of glacial deposits. These deposits overlie Proterzoic Grenvillian metamorphic rocks similar to the Adirondack region.
The St. Lawrence Valley region was completely covered by thousands of feet of ices from the Laurentide glaciers of the Pleistocene Epoch. The softer sedimentary materials were more easily scoured by the southward-moving continental ice sheets, creating lower bedrock topography than the harder, more erosionally resistant ancient Precambrian metamorphic and igneous rocks of the Canadian Shield, Adirondacks, and northern Appalachians. As the final Wisconsinian-Stage ice sheet melted, the lowlands became the primary regional drainage from the Midcontinent to the Gulf of St. Lawrence.
The Canadian cities of Montreal, Ottawa, and Quebec Cities are within the St. Lawrence Valley Province.
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Fig. 47. Satellite image map of the St. Lawrence Valley Province, highlighted in light green. extends along the St. Lawrence River and lower Ottawa River valley, between Lake Ontario and the Gulf of St. Lawrence.
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