Geologic Map Colors

GSA time scale
Table 1. Suggested colors for geologic maps.
Geologic age
Basic color
Color combination
Quaternary
Yellow or no color (white) Tints of yellow (30% and 50% are best to use, except in narrow bands or very small areas) or no color (white).
Tertiary
Orange, yellowish orange, tan, brown Combinations of yellow and magenta, with proportionally more yellow than magenta.
Cretaceous
Yellow green or olive green Combinations of yellow and cyan, with proportionally more yellow than cyan; the addition of a small proportion of magenta produces olive greens.
Jurassic
Green Combinations of yellow and cyan in equal or nearly equal proportions. Note: in theory, this is the correct color for Jurassic; however, in practice it is well to lean toward the conventional ?blue greens? when possible.
Triassic
Blue green Combinations of yellow and cyan, with proportionally more cyan than yellow.
Permian
Blue Tints of cyan; a small proportion of magenta is often needed to increase contrast.
Pennsylvanian
Blue with red Combinations of cyan and magenta, with a much higher proportion of cyan than magenta.
Mississippian
Bluish purple Combinations of cyan and magenta, with the proportion of cyan only slightly higher than magenta.
Devonian
Grayish purple Combinations of equal or nearly equal proportions of magenta and cyan plus a low proportion of yellow.
Silurian
Reddish purple Combinations of magenta and cyan, with proportionally more magenta than cyan.
Ordovician
Subdued red Light tints of magenta or combinations of a high proportion of magenta with low proportions of yellow and cyan.
Cambrian
Reddish brown Combinations of magenta and yellow in equal or nearly equal proportions plus a low proportion of cyan.
Precambrian*
Olive brown, olive, gray, olive blue, reddish olive Combinations of equal or nearly equal proportions of yellow, magenta, and cyan.

*Includes Proterozoic and Archean.

 

Igneous and Volcanic Colors

The colors used for igneous and volcanic units should contrast strongly with adjoining sedimentary units. Reds are generally preferred; however, any strongly saturated color may be used. Large areas should be in light tints of magenta; small areas should be in the brighter tints. In other words, the smaller the area, the brighter the color.

 

When To Break Color Standards

The age color scheme is most easily applied to geologic maps that do not have many units of any one geologic age. On large geologic maps that have many map units, it is sometimes impossible to maintain the standard geologic age colors. Some of the ways to modify the color selections for complex or otherwise challenging maps are described below.

A common problem is when there are map units of many geologic ages on the map, but one or more ages have too many units. To solve this problem, select colors that maintain the relative order of colors on the geologic age column but move up and (or) down on the column. For example, for a geologic age that has too many units, use the color immediately above the geologic age color for the youngest units, the correct color for the middle units, and the color immediately below the geologic age for the older units.

Even when breaking color standards, it is important to maintain the modified spectral order of the colors so that the map reader is able to identify the relative age of the units by color. In other words, orange areas represent units younger than those that are green, and green areas represent units younger than those that are blue.

Another situation in which color standards need to be broken is when all of the map units are of one geologic age, and there aren?t enough different shades of the recommended color to show all of the different map units. An example is USGS map I?2225 (Moore, and Trusdell, 1991), which has about 120 map units, all of Quaternary age. Yellow could not be used to distinguish all 120 map units, so the entire spectrum of colors was used on this map.

From https://pubs.usgs.gov/tm/2005/11B01/05tm11b01.html


When making a color scheme in GIS, you will probably have to:


Last revision 11/20/2017