Telling Time at Grand Canyon National Park

Grand Canyon is one of the most superlative geologic locales in the world with a rock record spanning approximately one third of the planet’s history and important records of the Proterozoic Eon and Paleozoic Era.

The Grand Canyon Supergroup is a thick sequence of mostly sedimentary rocks deposited during the Proterozoic (between 729 and 1255 million years ago) and exposed in places in the eastern part of Grand Canyon.

The Layered Paleozoic Rocks are the nearly horizontal sedimentary units exposed in the upper portion of Grand Canyon’s rock walls. They were deposited during the Paleozoic Era between about 270 and 510 million years ago.

Significant unconformities, or gaps in the rock record that represent periods of missing time, are present between each of Grand Canyon’s three sets of rocks.