1. Simple Bouguer gravity map of the Monrovia quadrangle, Liberia [cartographic material] Yale Public content 1974. 2013-04-03T18:00:23Z. 2013-04-10T17:34:11Z. Behrendt, John C., 1932-. U.S. Geological Survey. English. Public. Liberia and Monrovia Region.