Prelude

As the Atlantic Ocean began to form with the rifting of the Pangea supercontinent, our world's modern geography started to take shape. Rocks of Mesozoic age record this transformation and are spread across the U.S.A., from California to the Atlantic Ocean. On the East Coast, the Appalachian/Caledonian Mountains were split in two as the newly formed ocean basin formed. Triassic and Jurassic rift basins filled with thick sequences of stream sediments and evaporites. In the western U.S.A., several subduction-related orogenies occurred throughout the Mesozoic and formed many different mountain ranges and landscapes. Rocks of this age form much of the spectacular scenery of the western U.S.A., including the plutonic rocks of the Sierra Nevada Mountains, sedimentary rocks of Zion National Park, the Petrified Forest National Park, etc. (see Figure 12-1).

The Mesozoic was also an era that included animals that have long captured our imagination. Although dinosaurs dominated the land during much of this time, many other types of animals occupied the air and water. Pterosaurs filled the skies, with birds appearing in the Jurassic. Marine reptiles and sharks prowled the oceans. Mammals first made their appearance during the Triassic, but their survival depended on their keeping a low profile. Life was truly flourishing on Earth by the end of the Jurassic Period.

Wutpatki NM

Zion NP

Figure 12-1. Triassic and Jurassic rocks are exposed across the southwestern U.S.A.

Northeast of Flagstaff, Arizona, the Wupatki ruins were built from the reddish mudstones and sandstones of the late Triassic Moenkopi Formation (left).
Cross bedded Jurassic Navajo Sandstone dominates the Clear Creek area of Zion National Park, Utah (right).

Remember to click on the highlighted images to see larger versions.

What Will You Do Today?

Vermillion Cliffs

Explore the geologic history of the Triassic and Jurassic Periods of the Mesozoic Era

A. The Triassic & Jurassic Periods - Review the Triassic and Jurassic portion of geologic time

B. Triassic & Jurassic Geology and Life Forms - Learn more about Triassic and Jurassic geology and life forms

C. Hartford Basin & Zion National Park Geology - Explore two geologic maps that have Triassic and Jurassic rocks and structures

D. Geology of the Zion Canyon Area - Decipher the geologic history of the Zion Canyon area