“…These units accumulated in tidal flats and represent the initial transgression of the Cretaceous sea during the Albian (May, 1992). While most authors consider the "rusty beds" the basal part of the Thermopolis Shale (Washburne, 1908;Burk, 1956;Eicher, 1960Eicher, , 1962Mirsky, 1962;May 1992;May and others 1995), Love (1948) and Keefer and Troyer (1964) included the "rusty beds" with the underlying Cloverly Formation. The Thermopolis Shale, including the "rusty beds," ranges in thickness from 90 to about 220 ft.…”