Crazily Colorful Geological Maps of National Parks (and How to Read Them)

Like much of Alaska, the geology of this park is a complicated mix of large pieces of crust known as terranes that came from different places and were pushed together. Overlap faults are the result of a piece of crust pushed over each other, and they are shown on geologic maps as a black line with black triangular teeth on the side that was pushed up.

Normal faults, where the ground on one side of the fault slides down relative to the ground on the other side, are marked with black lines that become dotted where the fault is not visible on the surface. The strike-slip faults look the same, but have arrows on either side of the line to show that the crust on one side of the fault slides horizontally with respect to the crust on the other side.

The legend for this map contains other interesting symbols for dikes, calderas, ash, glaciers, and historic glacier expanses.

Great Smoky Mountains National Park

Geological map of the Great Smoky Mountains National Park area, Tennessee and North Carolina [Geologic map of the Great Smoky Mountains National Park region, Tennessee and North Carolina]USGS

The amount of detail in this map makes it look different and denser than the other maps in this gallery. It may seem messy, but each of these little dots and dots is geological information. In the close-up of the map to the right, you can see that most of the small marks are lines with a number next to them. These are direction and dip symbols that geologists use to indicate in which direction a layer of rock extends into the crust below.

strike_and_dipSedimentary rocks are deposited horizontally, but are often later tilted by tectonic forces. When geologists find a sedimentary layer, they use a special compass that has a leveling bubble and what is called an inclinometer, to find the maximum angle of inclination of the layer. The numbers next to the small lines are dip measurements, and the direction of the dip is indicated by a small check mark on the side of the line. The line represents the direction, which is parallel to the direction of the dip. Using these measurements, geologists can get a picture of what is going on below the surface to help them make cross sections like the one above.

In the example on the right, you can see that most keystrokes are done diagonally up and to the right. The dip measurements in the beige zone indicate that the layers dip to the left of the strike. But in the blue area on the left, the beds dip in the opposite direction. Between the two areas, you will see that there is an overlapping rift that pushed the blue formation above the beige formation.

Bryce Canyon National Park

Geological map of Bryce Canyon National Park and surrounding area, southwestern UtahUSGS / NPS

Like Arches National Park, much of the landscape in this park has been sculpted by wind and water erosion over time. Bryce’s crazy-looking arrows, known as fairy chimneys, have also been eroded by a process known as frost-wedging, where water trapped in cracks in the rock freezes, expands and pushes the crack further, eventually shattering pieces of rock.

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