November 18, 2012 A Slice of Heaven in Zion, Utah
The ancient rocks of Zion National Park in the southwest corner of Utah tell the story of the last quarter billion years. Water – whether salt or fresh – has played an enormous role in creating and ultimately shaping this magnificent landscape.
The history of Zion began before the first dinosaurs. There are nine different distinct layers of sedimentary rock within the park. Each formation is unique in its composition, revealing the secret of time with its geography, climate, plants and animals that lived during each period. Scientists have been able to reconstruct the past from these rich formations.
The climate is semi-arid with canyons receiving about 13 inches (325 millimeters) of precipitation a year and cliff-tops getting about twice that amount of moisture. There are three different species of cactus and two different kinds of yuccas at the lower elevations of 3,281 feet (1,000 meters) above sea level where it is hot and dry. The mid-elevation slopes are dotted with clumps of woodland pinyon pine and junipers. There are big ponderosa pines, Gamble’s oaks, Douglas and white firs and aspen’s at the higher elevations of 7,874 feet (2,400 meters) above sea level. Summers are hot and it snows here in the winter.
The oldest sediments in Zion were laid down 250 million years ago by a vast Permian Sea. Skeletons from millions of small creatures accumulated on the seafloor, fossilized and eventually formed the Kaibab limestone.
During most of the Triassic Period, from 245 to 210 million years ago, Zion remained flat and nearly featureless inundated by successive seas. It was also teaming with marine life now fossilized. The red-bed, iron-rich siltstones are clearly visible as banded strata. They are called Moenkopi after Moenkopi, Arizona where they were first discovered.
The most striking feature of Zion is without a doubt the towering Navajo sandstones displaying creams, pinks and reds. The Navajo sandstone formation reaches its maximum depth of 700 meters in Zion. This formation stretches all the way to Wyoming where it is called Nugget sandstone and into Nevada where it is known as Aztec sandstone.
The Navajo sandstone is made up of sand loosely cemented by iron oxide and to a lesser degree calcium carbonate.
One hundred and eighty million years ago present-day North America was much closer to the equator. It was extremely hot and very dry. A period of desertification lasted 10 million years and massive sand dunes piled-up high in the Navajo Desert. The desert covered an area of about 90, 734 square miles (235,000 square kilometers) extending from Wyoming to southeast California. It was much larger than the Sahara Desert of west Africa.
The very top layer or formation in the park is called the temple cap and it carried red mud during a brief flooding period at the end of the Navajo formation. It is about 246 feet (75 meters) thick. When the red color leaches out, as precipitation seeps through it over time, it dramatically stains the Navajo sandstone. On the huge rock named West Temple the red staining has been aptly called The Altar of Sacrifice.
Over the past two million years the Virgin River has carved itself into 4,265 feet (1,300 meters) of sandstones and siltstones forming awesome slot canyons.
Along the face of some canyons are hanging gardens where water seeps from the vertical walls and immense banks of maidenhair ferns and grasses have accumulated. In the spring and autumn golden columbines, shooting stars, purple violets and monkey flowers form a kaleidoscope of colors in Zion.
There are amazing small swamps next to the Virgin River with a species of endemic snail only found in the park.
A three and a half hour drive from Las Vegas is very worthwhile because there is no other place on Earth like Zion.
Text © by Dr Reese Halter 2012. All rights reserved.
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