Geologic map

A geologic map is a special-purpose map made for the purpose of showing subsurface geological features. In the United States, geologic maps are usually superimposed over a topographic map (and at times over other base maps) with the addition of a color mask with letter symbols to represent the kind of geologic unit, stratigraphic contour lines, fault lines, strike and dip symbols, and various additional symbols as indicated by the map key.

External links

• Geologic Maps from USGS National Park Service
• USGS National Geologic Map Database