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The Structure of Geologic Time

The Geologic Epochs of Time

Eons > Eras > Periods > Epochs

The Tertiary and Quaternary Periods of the Cenozoic Era are further divided into Time intervals called Epochs. The Epochs assist geologists and paleontologists in further specifying the conditions related to that particular Time.

The earliest Epochs of the Cenozoic Era occurred in the Tertiary Period. These Epochs are the Paleocene, Eocene, Oligocene, Miocene, and Pliocene.

In the image at right are the Epochs of the Quaternary Period. Currently, the Pleistocene and Holocene Epochs are the only two Epochs identified in the Quaternary Period. The advent of the Ice Ages is the significant event that identified the Pleistocene Epoch. The Holocene Epoch marks the conclusion of the Ice Ages and the initiation the modern warmer and dryer climate.

Of importance in the Tertiary and
Quaternary Periods are the Miocene Epoch,
the Pliocene Epoch, and the Pleistocene Epoch.


The Miocene Epoch lasted from 23.8 - 5.3 Million Years Ago in Idaho and was marked by the elephant-like Gomphothere that existed in Owyhee County.

The Pliocene Epoch from 5.3 Million to 1.8 Million Years Ago was marked in Idaho by the appearance of Lake Idaho in the vicinity of Hagerman, Idaho. During this Epoch, the horse, Equus simplicidens, existed.

The Pleistocene Epoch from 1.8 Million to 10,000 Years Ago is the first Epoch of the Quaternary Period and was marked by the most recent Ice Ages, remember that previous Ice Ages had occurred. During the Pleistocene Epoch the Mammoth, mastodon, sabre-tooth cat, lion, camel, llama, dire wolf, bison, coyote, ground sloth, caribou, and woodland muskox all survived on the Snake River Plain of Idaho.