Structures In Rocks Topics

Mapping Geologic Structures (Part 2)

Geologic Maps and Cross Sections

• Geologic maps are important tools for understanding geologic structures.  They also help geologists find important economic minerals and avoid hazards.

• Geologic maps are maps of the earth’s surface showing the types and ages of rock exposed.  Maps can also show structures.

Geologic Map
A portion of the Geologic Map of Virginia showing Shenandoah County (Division of Geology and Mineral Resources)

MapGeologic maps show the geology of the surface of the earth.  This map shows the geology of Shenandoah County.  Each color and pattern represents a different type or age of rock.  Each rock type is labeled with an abbreviation that stands for its age and formation name.  For example, Dma (oval) stands for the Devonian Mahantango Formation. 

408 to 360 million years ago

• Cross sections show the geology of a vertical plane below the earth’s surface.  Cross sections are valuable tools for visualizing structures. 

Cross Section
Map and cross section courtesy of the Division of Geology and Mineral Resources

Geologic cross sections are representations of underground geology.  Geologists use geologic maps with structural symbols, like the map of the Salem area to create cross-sections (above).  The line (D-D’) on the map is the line along which the cross section was drawn.  Anticlines, synclines, and faults can be seen in cross sections.