The park is situated on a rugged peninsula of thick forests, many lakes, high granite cliffs, and the most dramatic heights and lookouts in the province. The profile of the southern part of the peninsula, when viewed from Thunder Bay, resembles the figure of a sleeping giant lying on his back -- hence the park's name. Deep valleys and fast-running clear streams characterize the terrain.

From a geological standpoint, Sleeping Giant can be described as a huge layer cake. The bottom of the cake was laid down as sedimentary rock about 1.7 billion years ago, in the Middle Precambrian era, when much of North America was submerged beneath a giant sea. A second sedimentary layer was added in the Late Precambrian era about 1.3 billion years ago. Later, a filling of molten rock squeezed between the layers, hardening as diabase sills. Then came more sedimentary layers and more diabase intrusions. Eons of erosion and several periods of glaciation have worn away the soft sedimentary icing, leaving five flat-topped mesas of erosion-resistant diabase.

The park is part of the northern boreal forest, but it lies at the northern and eastern limits of many southern and western plants. The result is an exceptional mix of plant life. Cloudberry, arctic bistort and butterwort grow hundreds of kilometres south of their usual arctic habitat. A bog in the park's southern end supports two rare orchids -- the adder's mouth and the striped, round-leaved orchis. Some 24 types of orchid grow here, including arethusa, calypso, and the plentiful pink lady's slipper. Ferns also abound.

The park is home to a wide range of wildlife including white-tailed deer, red fox and porcupine, moose, bears, wolf and lynx. More than 190 species of birds have been recorded at Sleeping Giant.