||Mesozoic rocks and Pleistocene morainal deposits underlie the Southwestern Upland. The Porcupine, Duck and Riding Mountains, whose eastern sides form the steepest parts of the Manitoba Escarpment, are separated in turn by broad gentle valleys. Turtle Mountain is an erosional remnant capped by Paleozoic sandy silty shales containing sub-economic deposits of lignite, and by Pleistocene glacial moraines.
Mesozoic formations consist almost entirely of shales and sandstones, with some limestones and gypsum. Maximum thickness of Mesozoic beds in the southwestern corner of the province is approximately 1070m. Numerous channel-filled deposits of Mesozoic sediments also occur within the Paleozoic outcrop belt.
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