Geological Faults, Folds, and Map Symbols: Key Concepts

Normal fault

Hanging wall down (left)

Reverse fault

Hanging wall up (left)

Strike-slip fault

The direction of the line formed by the intersection of a rock surface with a horizontal plane

Dip fault

Acute angle that a rock surface makes with a horizontal plane

Oblique Fault

moves both vertically and horizontally

Anticlines

Oldest unit is in the middle at the bottom of the anticline

Synclines

Youngest is at the top in the middle of the syncline

Basins

Youngest in the middle; Oldest is exposed on the outer surface

Domes

Oldest is exposed on the surface in the middle; Youngest is exposed on the outer surface

Color on geologic map

Each color represents a separate geologic age

Symbols on geologic map

First letter indicates age; Second and third letter indicates the rock name/type

Numbers on geologic map

Represent Elevation