The grey rocks exposed in the cliffs on the upper part of Crowsnest Mountain are
limestones and
shales of
Late Devonian to
Early Mississippian age (the
Palliser at the base, overlain by the
Exshaw and
Banff, with the
Livingstone Formation at the summit). They were moved up from the west along the Lewis
thrust fault and emplaced over younger rocks (the
Late Cretaceous Belly River Formation) that underlie the wooded lower slopes of the mountain. During that movement they were formed into a broad
syncline by
fault-bend folding. The Devonian to Mississippian rocks are part of the Lewis
thrust sheet which was originally continuous from the
High Rock Range immediately to the west. The thrust sheet has since been cut through by erosion along Allison Creek, however, leaving Crowsnest Mountain and its northerly neighbour,
Seven Sisters Mountain, standing together as an isolated
klippe. ==References==