May 2013 Archives

EEAS Tour of Southwestern US Geology

From May 12­ - 18, EEAS Professors Lori Weeden and Kate Swanger took seven students on a whirlwind tour of southwestern geology.  To bring you this report on the geologic history of Utah and Arizona, these nine brave souls had to endure ridiculously picturesque scenery, excessive laughter on long van rides, and delicious s?mores cooked over the campfire. It was a most perilous expedition.

Zion National Park, southwestern Utah.

At our first stop we marveled at the 2,000-ft high cliffs of Navajo Sandstone in Zion NP. These rust-colored sandstones were deposited during the Jurassic, when stegosaurs and brachiosaurs roamed our continent, and Utah was buried under a massive expanse of sand dunes. All of the continents had come together to form one supercontinent, Pangaea, and the colossal Appalachian Mountains (still young and as tall as the present-day Rockies), were shielding the western US from rain, causing a vast desert to form in Utah.

At Zion NP the students braved steep cliffs to hike the famous Angel?s Landing Trail. On this hike, we got a close-up view of the large-scale cross-beds of the Navajo Sandstone, formed as sand dunes migrated and buried each other.  We could also clearly see the gradation of brown to pink to white in the Navajo, which is caused by variations in the oxide minerals that cement this impressive deposit.



Left: Zion National Park, southern Utah. Right: Cameron Simmons poses next to chevron folds in Kolob Canyon, Zion National Park.

Bryce National Park, southwestern Utah

After the break-up of Pangaea, 200 million years ago, North America was inundated by a massive inland sea that covered much of the interior of our country, including Utah. In this warm, lush environment, dinosaurs still ruled North America. But ?all good things must come to an end.? By the time the Yucatan Peninsula was hit by an asteroid 65 million years ago (marking the end of the dinosaurs), the waters were already retreating from the interior of the US. The Rocky Mountains were beginning to rise, and along with them the Colorado Plateau where Bryce NP and Grand Canyon NP now reside.  From 70­?40 million years ago, as Utah emerged from the ocean, vast fluvial and lake deposits were formed, including the sandstones, siltstones and limestones that would eventually form the famous ?hoodoos? of Bryce NP.  These hoodoos (or spires) formed during the past few million years, as wind and water eroded vertical fractures in the rocks, making Bryce NP one of the most unique and gorgeous landscapes on Earth.


Left: Alison O'Connor and Dylan Cole hike through Bryce Canyon National Park, southern Utah. Right: Ryan Farrell investigates the Claron Formation limestones in Bryce Canyon National park.

Grand Canyon, northern Arizona

Carved by the mighty Colorado River during the past six million years, the Grand Canyon has beckoned tourists, adventurers, and artists from around the globe. It stands as a clear testimony of the power and antiquity of the Earth we live on, reminding us that we are but tiny pieces in a greater whole that has existed for billions of years and that will continue to exist long after we are gone.

Our first glimpse into the Grand Canyon came after a long van ride, when we stopped along the eastern South Rim. Though exhausted, we were enraptured by its beautiful enormity and couldn?t wait to hike down Bright Angel Trail the following day. Along with pack-mules, horses and hundreds of other travellers, we literally hiked backward through time, starting with the 270-million year old Kaibab Limestone that caps the South Rim, down to the 505-million year old Muav Limestone.  Had we more time and endurance, we could have hiked all of the way down to the Vishnu Schist, a 1.7-billion year old rock that forms the ?basement? of the southwest. Every year, thousands of hikers take this journey, hiking ?rim to rim,? traversing 1.5 billion years of earth history in less than a day.


From left to right: Rachael Megnia, Kate Swanger, Cameron Simmons, Tara Cenzalli, Ryan Farrell, Lori Weeden, Sephera Simoneau, Alison O’Connor, and Dylan Cole on the South Rim of the Grand Canyon, northern Arizona.

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