Canadian Shield is a huge, rocky region that curves around Hudson Bay like a giant horseshoe. The Shield covers about half the land area of Canada. It includes most of Baffin Island; all of Labrador; nine-tenths of Quebec; over half of Ontario and Manitoba; large areas of Saskatchewan, Nunavut, and the Northwest Territories; and the northeastern corner of Alberta. About 1,771,000 square miles (4,587,000 square kilometers) of the Shield’s area lie in Canada.
In the north, the Canadian Shield also extends beyond Baffin Island to cover most of Greenland, which was part of the continental mainland of North America before it broke away millions of years ago. In the south, the Shield dips into the United States to form the Adirondack Mountains of New York and the Superior Uplands of Michigan, Wisconsin, and Minnesota. Including these regions, the total area of the Shield is about 3 million square miles (8 million square kilometers).The Canadian Shield is also called the Laurentian Plateau, after the Laurentian Mountains of southern Quebec.
The Canadian Shield consists of a large area where extremely ancient rock lies at Earth’s surface. Geologists estimate that the rock formations that make up most of the Canadian Shield range in age from about 540 million years to more than 4 billion years old. Most of the rocks have undergone one or more periods of mountain-building. During these periods, extreme heat and pressure produced high mountains of granite, diorite, quartzite, and other crystalline rocks. Weathering and erosion wore down the mountains to expose the ancient rock beneath.
Today, much of the Canadian Shield’s central and northwestern part is low and flat. Mountains in the northeastern part of the Shield rise as high as 8,500 feet (2,590 meters). 
Relatively few people live in the region. Only small areas are suitable for agriculture. The Shield is dotted with lakes, some of which have become famous resorts. Large forests in the southern section rank among Canada’s most important natural resources. The Canadian Shield is also rich in copper, gold, iron, nickel, uranium, and other minerals.
