The last of the glaciers receded from Quetico about 12,000 years ago, leaving a landscape dominated by exposed bedrock, rounded, smoothed or scratched, crushed into boulders or shattered to form imposing cliffs.

The visitor to Quetico will find a primeval wilderness of limitless forests, mirror-smooth lakes, and innumerable bogs, all supporting a rich variety of plants and animals. The northern forest is mainly black spruce, jack pine, trembling aspen and white birch, with sheltered pockets of more southern trees such as oak, elm, silver maple, yellow birch and basswood. The park also has magnificent stands of red and white pine. Red squirrels, chipmunks, beaver and mink are among the smaller mammals. Larger species such as wolf, bear and moose also live here, and in summer more than 90 species of birds nest in the park.

Quetico's many interconnecting waterways were the highway system upon which explorers sought the passage to the West. They were also a vital transportation route that supplied tons of fur pelts to the markets of Montreal and Europe in the mid-17th century. Today these waterways are a wilderness paradise for canoeists.