The rocks that form the Canadian Shield were formed about two billion years ago, when they were under water in the Precambrian era. The rocks are mostly sedimentary, though there are some igneous rocks that date back 1.25 to 1.5 billion years. More recent rocks that were formed above these ancient layers were removed by the scouring action of glaciers that covered northern North America in the several ice ages in the past 100,000 years.
The last ice age scraped the rocks in a NNE (north-north-east) to SSE
(south-south-east) direction. The soil on which the grasses and other vegetation
grow in this part of the continent are the result of gradual sediment
buildup since the last ice age.
Saskatoon lies at the boundary where the wide open plains meets the Canadian Shield. The area north of Saskatoon is rugged northern boreal forest, with many lakes and vast forests. The area south has accumulations of fertile soil that has accumulated over many centuries on top of the glacier-scoured rock.
More history of Saskatoon