National Geologic Map Database

This page describes how to optimize your searches in Geolex when searching for geologic units by name, location, or geologic age. Every geologic unit in Geolex will be returned unless you specify criteria to narrow your search. The search count will update automatically as you enter your criteria indicating how many hits will be returned when the form is submitted.

Unit name

Use this field to search Geolex for units or associated units starting with the search term entered. The search engine will return both a listing of direct unit name matches, and a listing of units where your search term was found in the unit description, or "usage", field.

Lithologic characteristics (e.g. "formation" or "limestone") can be included as part of the unit name. In the latter case the search will repeat, as necessary, removing the last word of the input unit name, until a match is found. Upper and lower case characters are considered equal so either may be used.

Unit name search field image
  • Examples:
  • dakota — returns all units starting with "Dakota" and any units containing the term "Dakota" in the usage field.
  • dakota sandstone — returns all units starting with "Dakota" and any units containing the term "Dakota Sandstone" in the usage field.
  • Dak — returns all units names starting with "Dak" ("Dake", "Dakin Hill", "Dakota") and any units containing the term "Dak" in the usage field.

— Will empty the unit names field completely

State or Territory
Unit name search field image

Click on the map to select units based on their appearance in published products for a particular state or territory. By default, all locations are assumed if none are selected.

This lexicon lists only a few Canadian and Mexican units that extend across the border into the U.S. If you need more detailed information for Canada or Mexico, click the appropriate button below the map.

— Resets the Map (selecting all states and territories)

Geologic Age Range
Unit name search field image

The timescale on the Geolex search page shows the youngest ages at the top and the oldest ages at the bottom. By default, all ages have been selected.

Select a geologic age range by dragging the range sliders up or down. You may also click on the timescale to re-position the slider handles. Check marks will appear beside all ages to be included in your search. Period names will be selected once all Epochs names for that period have been selected. Similarly, Era names will become selected when all Period names have been chosen.

Some more recently defined (or redefined) epochs, such as the Early, Late, and Middle Permian, are not yet searchable in Geolex (see Geologic Time Scales page for explanation). Note in the example below that although the range sliders extend from the Late Permian Epoch (oldest) to the Early Jurassic Epoch (youngest) the entire Permian Period will be included in the search as indicated by the check marks.

— Resets the timescale (selecting all ages)

Unit name search field image

For more information on the Geologic time scale as it pertains to Geolex, please visit the Geologic Time Scales page.

Publications cited in Geolex

Geolex is a tool for discovering information about geologic units. We recommend searching the Map Catalog if you are interested in finding publications that are cited in Geolex, and need to search for them using criteria such as title, author, publisher, etc.

Clicking the link illustrated below will open the Map Catalog search form with the "Cited in Geolex Database" option pre-checked as shown in the image to the right. This will limit your search to only those records cited in Geolex. Note that clearing the Map Catalog search form will expose all records in the Map Catalog, and you will need to re-check the Geolex check box if you still wish to limit your search to Geolex records.

catalog search image
Unit name search field image