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Geologic Map Colors:
U.S. Geological Survey Standard

In general, these colors apply only to sedimentary rocks, and plain colors apply only to marine rocks. Sedimentary rocks that form on land are depicted with these colors plus patterns, such as dots or stripes.

The other major rock classes—igneous and metamorphic—have their own color traditions, rather than standards. Reds and oranges are reserved for the igneous rocks: volcanics take orange while plutonics take red, and in both of these older rocks are shown with darker colors. Metamorphic rocks tend toward browns, olives, and other "complex" colors. All of them use patterns freely as well. This makes the production of geologic maps, whether for print or online publication, a skilled art.

These colors are those specified by the current standards of the U.S. Geological Survey, which tend to govern maps produced by the individual states and American scientists. Their history goes back to the 1880s (see older color lists). For the time spans associated with these units, see the Phanerozoic geologic time scale and the Precambrian geologic time scale. The International Commission on Stratigraphy maintained its own color standard for many years with a notably different esthetic, particularly in the Precambrian. In 2009 the Committee for the Geologic Map of the World issued a new color standard that split the difference between the two. All of my geologic time scales use that standard, but old maps reflect the standards of the nation and time that produced them.

Eon
Era
Period
Epoch
PhanerozoicCenozoicQuaternaryHolocene
Pleistocene
NeogenePliocene
Miocene
PaleogeneOligocene
Eocene
Paleocene
MesozoicCretaceousUpper Cretaceous
Lower Cretaceous
JurassicUpper Jurassic
Middle Jurassic
Lower Jurassic
TriassicUpper Triassic
Middle Triassic
Lower Triassic
PaleozoicPermianLopingian
Guadalupian
Cisuralian
CarboniferousPennsylvanian
Mississippian
DevonianUpper Devonian
Middle Devonian
Lower Devonian
SilurianPridoli
Ludlow
Wenlock
Llandovery
OrdovicianUpper Ordovician
Middle Ordovician
Lower Ordovician
CambrianUpper Cambrian
Middle Cambrian
Lower Cambrian
ProterozoicNeoproterozoicEdiacaran
Cryogenian
Tonian
MesoproterozoicStenian
Ectasian
Calymmian
PaleoproterozoicStatherian
Orosirian
Rhyacian
Siderian
ArcheanNeoarchean
Mesoarchean
Paleoarchean
Eoarchean
Undifferentiated Precambrian time
Eon
Era
Period
Epoch
(c) 2005 Andrew Alden, licensed to About.com, Inc. Data from Geologic Time Scale of 2004. (fair use policy)

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