Geology 101 - Introduction to Physical Geology
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Tables of Geologic Map Symbols

Strike and Dip Symbols
Strike and dip are a way of representing the three-dimensional orientation of a planar surface on a two-dimensional map. The strike is the compass direction of a horizontal line on the plane. All the horizontal lines on a plane are parallel, so they all have the same characteristic compass direction. The dip is the angle at which the plane slopes downhill from the horizontal, at its maximum slope, which is at right angles (90) from strike.
Map Symbol Definition Explanation of symbol
strike and dip of beds other than horizontal or vertical
  • strike (longer line) is horizontal line on bedding plane
  • strike parallels nearby contacts between stratified rocks
  • dip shows which way beds run downhill
  • dip angle, number at end of dip symbol, is how much beds tilt down from horizontal
horizontal beds
  • because the bed is horizontal it strikes in all directions
  • because the bed is horizontal, the dip is 0%
strike and dip of vertical beds
  • strike (longer line) is horizontal line on bedding plane
  • because the bed dips vertically (has a 90% dip), it dips equally in either direction at right angles to strike, so the dip line is shown extending in both directions

Geologic Fault Symbols
Type of Fault Map Symbol Definition Type of Regional Stress Geologic Associations
normal hanging wall down, footwall up tension
  • zones of crustal extension
  • divergent plate boundaries
  • edges of horsts and grabens
  • Basin and Range region
detachment low-angle normal fault, footwall - gneiss, hanging wall - shallow-crust rocks tension
  • boundaries of metamorphic core complexes
thrust hanging wall up, footwall down compression
  • zones of crustal compression
  • convergent plate boundaries
reverse high-angle (45° or more dip) thrust fault compression
  • zones of crustal compression
  • convergent plate boundaries
strike-slip rocks on either side move horizontally in opposite directions shear
  • continental margins undergoing oblique (not straight on) plate convergence
  • transform plate boundaries
oblique-slip combines horizontal and vertical motion combination
  • orogenic mountain belts
  • continental margins undergoing oblique (not straight on) plate convergence

Geologic Fold Symbols
Type of Fold Map Symbol Definition Appearance of Beds in Map View
anticline up fold
  • roughly parallel stripes
  • dip away from center (away from axis)
  • oldest at center (along axis)
  • youngest farthest from center
plunging anticline up fold with tilted axis
  • roughly a U-shaped pattern
  • plunges in direction U points
  • oldest at center (along axis)
  • youngest farthest from center
syncline down fold
  • roughly parallel stripes
  • dip toward center (toward axis)
  • oldest farthest from center
  • youngest at center (along axis)
plunging syncline down fold with tilted axis
  • roughly a U-shaped pattern
  • plunges in direction U opens
  • oldest farthest from center
  • youngest at center (along axis)
monocline strata tilted in one direction
  • all dip in same direction
structural dome upward bulge in layered rocks
  • roughly a bull's eye pattern
  • dip away from center
  • oldest in center
  • youngest farthest from center
structural basin downward bulge in layered rocks
  • roughly a bull's eye pattern
  • dip toward center
  • youngest in center
  • oldest farthest from center

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Geology 101 - Introduction to Physical Geology
Basics Table--Geologic Map Symbols
Created by Ralph L. Dawes, Ph.D. and Cheryl D. Dawes, including figures unless otherwise noted
updated: 7/10/11

Unless otherwise specified, this work by Washington State Colleges is licensed under a Creative Commons Attribution 3.0 United States License.

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