Erosion was accelerated during the Ice Ages by four glacial advances and retreats. But the glaciers did leave their own telltale layer of unconsolidated sediments. Formed during the Pleistocene Epoch, the uppermost layer of the valley walls varies in thickness from less than a metre to a hundred metres. Between the Pleistocene and the Late Cretaceous layers is a time gap of at least 64 million years. The exposed sedimentary rock layers along the Red Deer River Valley around Drumheller are referred to as the Horseshoe Canyon Formation.
Black layers are coal seams.
Dark gray layers are mudstone. Lighter gray layers are sandstone. As these layers continue to erode, fragments of dinosaur bone, petrified wood and are other fossils are exposed. Some 25 species of dinosaurs have been discovered in these badlands since 1884 when Joseph Burr Tyrrell , the Museum's namesake, discovered the first Albertosaurus skull. This document was prepared by Wayne Hortensius, Calgary, Alberta, Canada for the Royal Tyrrell Museum Cooperating Society.