Different Times, Different Environment Activity Source: Organizing partners of Geologic Map Day are the U.S. Geological Survey, the Association of American State Geologists, the National Park Service, the Geological Society of America, NASA, and the American Geosciences Institute. Geologic maps show the locations of various kinds of rocks at the surface. In places where rivers have eroded the surface, deeper layers become exposed. The opposite occurs when lake levels rise; rocks along the shore are covered by water. [Read More]