A thick sequence of shales, siltstones and mudstones overlay the marine Bearpaw Formation, including the Hell Creek, Bear, Lebo and Melville Formations which span the Laramide Orogeny. The Melville is the most coarse grained of these formations (Simpson, 1937). On top of these sequence is the early Eocene (~54 mya) Lindley Conglomerate containing volcanic material derived from the Absaroka region to the west. Both the Castle and Crazy Mountains arose at this later date (Thom, 1957).