National Geologic Map Database

Because of the federal government shutdown, ngmdb.usgs.gov is not being updated and the agency will not be able to respond to inquiries until appropriations are enacted. For more information please visit: https://www.doi.gov/shutdown

			USGS HOME	CONTACT USGS	SEARCH USGS

Home Catalog Lexicon MapView TopoView National Geology New Mapping Standards Comments

National Geologic Map Database
Geolex Search

Search Count

updating count

Units

Search Reset

Geologic Age Range Search by geologic age

ERA	PERIOD		EPOCH
Cenozoic	Quaternary		Holocene
	Quaternary		Pleistocene
	Tertiary	late (Neogene)	Pliocene
		late (Neogene)	Miocene
		early (Paleogene)	Oligocene
			Eocene
			Paleocene
Mesozoic	Cretaceous		Late
	Cretaceous		Early
	Jurassic		Late
			Middle
			Early
	Triassic		Late
			Middle
			Early
Paleozoic	Permian		Late
			Middle
			Early
	Carbonif.	Penn.	Late
			Middle
			Early
		Miss.	Late
			Middle
			Early
	Devonian		Late
			Middle
			Early
	Silurian		Late
	Silurian		Early
	Ordovician		Late
			Middle
			Early
	Cambrian		Late
			Middle
			Early
Precamb. **	Proterozoic **		Late *
			Middle *
			Early *
	Archean **

** Eon. * Era. Learn more

Welcome

The U.S. Geologic Names Lexicon ("Geolex"), a National compilation of names and descriptions of geologic units.

Find additional
Stratigraphic Resources

Search NGMDB for
publications cited in Geolex

Unit Name Search by unit name, or skip to search all

State or Territory Click State/Territory to search, or skip to search all

Canada Lexicon Mexico Lexicon

Search Reset

Accessibility FOIA Privacy Policies and Notices

U.S. Department of the Interior | U.S. Geological Survey
Supported by the National Cooperative Geologic Mapping Program
Page Contact Information: Personnel
Page Last Modified: Sun Oct 5 06:25:13 2025