[5] The hills lie within the eastern portion of the Western Canadian Sedimentary Basin in an area where the Souris River Formation overlays the Precambrian bedrock.

During the Quaternary period, when the ice sheets advanced and retreated, these raised areas of bedrock snagged more glacial till than their surroundings, further increasing their height.

This canyon cuts through the layers of glacial till and the Devonian sediments creating substantial cliffs parallel to the river.

[2][9] The reserve protects the riparian zone of the Armit River and the adjacent uplands containing spruce forest, sphagnum meadows and fescue prairie.

[2] The reserve is within the Porcupine Hills Ecodistrict in the Mid-Boreal Uplands Ecoregion within the Boreal Plains Ecozone.