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Remarkable Arches National Park

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Remarkable Arches National Park
Moab, Utah

Arches National Park in southeastern Utah has the highest concentration of natural stone arches in the world with over 2,000 documented arches dotting the landscape.

The park sits atop an underground evaporite layer (salt bed). This salt bed was deposited in the Paradox Basin of the Colorado Plateau nearly 300 million years ago when an ocean flowed through the region. That sea eventually evaporated, leaving behind a desert environment and over the course of millions of years, the salt bed was covered with debris eroded from the Uncompahgre Uplift, including significant amounts of Navajo and Entrada Sandstone. This debris accumulated to over 5000 feet thick.

Arches National Park Utah

5000 feet of weight atop the salt bed below caused it to liquefy and bulge upward forming domes. The Entrada Sandstone above this swelling bed was once a massive desert, full of shifting dunes of fine-grained sand. The grains are nearly spherical so when they are packed together, they form a rock that is very porous. But the Carmel layer that formed beneath the sandstone was a mix of sand and clay particles. Clay particles are smaller, which allowed them to pack together well with porous sand particles to form a much denser rock.  Therefore under pressure, these strong rock layers above the salt bed were forced to crack.

Over time, water seeped into the cracks and folds of these layers and ice formed in the fissures. The expansion and contraction put pressure on the surrounding rock, breaking off bits and pieces, while winds cleaned out the loose particles. What remained were the free standing fins. Wind and water battered these fins until, in some, the water dissolved the calcite bonding in the sand so thoroughly, chunks of rock broke off. Many damaged fins just collapsed, while others, with the right degree of hardness and balance, survived despite their missing sections. These became the famous arches, which range from sliver-thin cracks to over 300 feet (97m) wide.

On average, the park receives 8-10 inches (18-23cm) of precipitation a year, which forms a delicate balance. If the park received too much precipitation, the sandstone could erode so quickly that arches would not have time to form. If it never rained, the erosion would stop.

The Arches area was first brought to the attention of the National Park Service by Frank A. Wadleigh, passenger traffic manager of the Denver and Rio Grande Western Railroad. Wadleigh visited the area in September 1923 and was impressed by what local prospector Alexander Ringhoffer showed him. He suggested to Park Service director Stephen T. Mather that the area be made a national monument. A succession of government investigators examined the area and the designation of a national monument was supported by the Park Service from 1926, but was resisted by President Calvin Coolidge’s Interior Secretary, Hubert Work. Finally in April 1929, shortly after his inauguration, President Herbert Hoover signed a presidential proclamation creating Arches National Monument. The purpose of the reservation under the 1906 Antiquities Act was to protect the arches, spires, balanced rocks, and other sandstone formations for their scientific and educational value.

In early 1969, just before leaving office, President Lyndon B. Johnson signed a proclamation substantially enlarging Arches. Two years later in 1971, President Richard Nixon signed legislation enacted by Congress which significantly reduced the total area enclosed, but changed its status to a National Park.

Arches National Park Utah

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