What is a Geologic Map?

Title Page
Introduction
What is a Geologic Map?
What is a Geologic Map Used For?
Why are Geologic Maps Important?
Hasn’t It Been Mapped Before?
What Do All Those Lines, Colors,
  and Symbols Represent?
How is a Geologic Map Made?
References

Geologic maps graphically communicate vast amounts of geologic information - they are to a geologist what blueprints are to an architect, what a highway map is to a traveler, or what a photo-realistic painting is to an artist.

Geologic maps display three-dimensional features on a flat piece of paper, with the added benefit of depicting the relative age, composition, and relationships among rocks and sediments at and near the earth’s surface.

A detailed geologic map shows what it is you are standing on; where similar rocks or sediments may be found; how old they are; what they are composed of; how they formed; how they have been affected by faulting, folding, or other geologic processes; and what existing or potential mineral resources and geologic hazards are nearby.

It would require volumes of text to describe what a geologic map can show on a single sheet of paper. It should come as no surprise then that geologic maps are the most fundamental and important geologic database for the earth sciences. They are the foundation for all other geologic studies.

There are many types of specialized geologic maps - for example, those that focus on bedrock geology, structure, geologic resources, geologic hazards, or the geology of surficial sediments. Most maps produced by the Utah Geological Survey (UGS) give equal weight to each of these factors and so are considered multi-purpose geologic maps.

Geologic mapping is commonly confused with surveying. Surveyors, however, use sophisticated measuring instruments to make a base map of an area - that is, a map that shows roads, buildings, and other cultural features; rivers, lakes, and other waterbodies; topography; and other information. Maps that surveyors make include highway and street maps, maps showing property ownership, topographic maps, and many other types of maps.

Cross section and explanation of Quail Creek Reservoir map.
Click to see larger figure.

Geologic maps are also often confused with shaded-relief or topographic maps, which show hills, valleys, roads, and other features on the Earth’s surface. Geologic maps, however, use a combination of colors, lines, and symbols to depict the composition, distribution, and relationships of rocks and sediments at and near the Earth’s surface.

Geologic maps are printed on a base map - which shows topography, roads, rivers, and other cultural and natural features - to allow users to accurately determine their location with respect to mapped geologic features.

Geologic maps normally include cross sections or block diagrams that reveal the structure or arrangement of rocks below the Earth’s surface. Such diagrams give map users a glimpse below the ground surface and a better understanding of the three-dimensional arrangement of the rocks. Understanding this third dimension is particularly important for the discovery and assessment of mineral and energy resources.