Map of prehistoric freshwater Lake Bonneville showing its main body and Sevier body, with the Provo water area marked in blue. Lake Bonneville was about 10 times larger than today’s Great Salt Lake which actually is a remnant of Lake Bonneville. The Provo shoreline was formed when the Lake levels stabilized following massive flooding out through Red Rock Pass. Towns and cities throughout the states of Utah and southeastern Idaho are drawn in to show their location on ground once covered by Lake Bonneville. State lines are clearly marked, as well as latitude/longitude. “Lake Bonneville Pl. XIII.” is written at the top right margin. Map was drawn by G. Thompson; printed by Julius Bien & Co. lith. Map colors are blue and black on ivory paper.