Glaciation has left the area with only a thin layer of soil, through which exposures of igneous bedrock resulting from its long volcanic history are frequently visible.

[1] The shield extends into the United States as the Adirondack Mountains (connected by the Frontenac Axis) and the Superior Upland.

The Canadian Shield is a U-shaped subsection of the Laurentia craton signifying the area of greatest glacial impact (scraping down to bare rock) creating the thin soils.

[4] The Canadian Shield is a collage of Archean plates and accreted juvenile arc terranes and sedimentary basins of the Proterozoic Eon that were progressively amalgamated during the interval 2.45–1.24 Ga, with the most substantial growth period occurring during the Trans-Hudson orogeny, between c. 1.90–1.80 Ga.[5] The Canadian Shield was the first part of North America to be permanently elevated above sea level and has remained almost wholly untouched by successive encroachments of the sea upon the continent.

During the Pleistocene Epoch, continental ice sheets depressed the land surface (creating Hudson Bay) but also tilted up its northeastern "rim" (the Torngat), scooped out thousands of lake basins, and carried away much of the region's soil.

The northeastern portion, however, became tilted up so that, in northern Labrador and Baffin Island, the land rises to more than 1,500 metres (5,000 feet) above sea level.

[8] The multitude of rivers and lakes in the region is classical example of a deranged drainage system, caused by the watersheds of the area being disturbed by glaciation and the effect of post-glacial rebound.

The Canadian Shield is part of an ancient continent called Arctica, which was formed about 2.5 Ga during the Neoarchean era.

The current surface expression of the shield is one of very thin soil lying on top of the bedrock, with many bare outcrops.

This arrangement was caused by severe glaciation during the ice ages that covered the shield and scraped the rock clean.

The shield is covered in parts by vast boreal forests in the south that support natural ecosystems as well as a major logging industry.

The boreal forest area gives way to the Eastern Canadian Shield taiga that covers northern Quebec and most of Labrador.

[19] In the case of polar bears (Ursus maritimus), the shield area contains many of their denning locations, such as the Wapusk National Park.