What is the Geologic Time Scale?

Much of the geographic and economic history of southern and eastern Idaho is controlled by its geology. Thus a basic understanding of that geologic history is necessary to more fully appreciate the state.

The discussion of the history of the earth requires reference to time periods of the past and their approximate ages. These terms, like "Proterozoic" and "Cretaceous," are not part of the vocabulary of normal Americans, and they can be intimidating.Use this Timeline and the Atlas Glossary to become more familiar with these terms.

The time spans and hierarchy of these geologic periods are shown in the Timeline Figure at left.

A great deal of information is also listed in the Southern Idaho Geologic Event Table (pages 8 and 9 of Rocks, Rails and Trails).

Use these materials to become familiar with the terms and concepts of the geologic time scale.