Geologic maps are used to identify important features and inform our decisions as we live among the Earth's dynamic, connected systems. Use the basemap (with the city's roads in the background) or the coordinate system grids along the border to find a location that interests you. Then, find out what geologic map unit (the type of rock or sediment) is at that location and go the map key for the explanation. You can look for line and point symbols on the map that show things like mines, well locations and contacts between units like scarps and faults. The map also reveals broad patterns that describe the Earth's history in the area.