7.2: Geological Maps and Cross-Sections
- Page ID
- 36912
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Geologic maps are two dimensional (2D) representations of geologic formations and structures at the Earth’s surface, including formations, faults, folds, inclined strata, and rock types. Formations are recognizable rock units. Each formation is indicated by a color and a label.
Cross-sections
Cross-sections are subsurface interpretations made from surface and subsurface measurements. Maps display geology in the horizontal plane while cross-sections show subsurface geology in the vertical plane.
Strike and Dip
Geologists use a special symbol called strike and dip to represent inclined beds. Strike and dip map symbols look like the capital letter T, with a short trunk and extra-wide top line. The short trunk represents the dip and the top line represents the strike. Strike is the direction the bed travels. Dip has two components.
Dip direction is the direction a ball would roll if set on the layer and released. Dip amount is how inclined from horizontal the layer is in degrees. A number next to the symbol represents the dip amount. A horizontal rock bed has a dip of 0° and a vertical bed has a dip of 90°.
- cross section – a vertical slice or profile through the Earth, showing the arrangement and relationships of rock layers, structures, and features beneath the surface
- dip – the angle at which a rock layer, fault, or other planar feature is inclined from the horizontal, measured downward in the direction of maximum slope
- map – a two-dimensional representation of the Earth’s surface used to show the distribution of rock units, structures, and landforms
- strike – the compass direction of the line formed by the intersection of a rock layer or planar feature with a horizontal surface