COLORADO PLATEAU AND A SANDSTONE RAINBOW

The Colorado Plateau is an area of uplifted land which includes Arizona, Utah, New Mexico, and Colorado, with Arizona and Utah having the largest sections. About 70 million years ago, geolic forces began to push the land upward. The largest uplift happened about 5.5 million years ago, which rose the area about 3000 feet above the surrounding landscape. This buckled the surface of the land, mountains pushed up and different water sources created shapes and forms, which makes the southwest unique, including arches, arroyos, canyons, cliffs, fins, natural bridges, pinnacles, and hoodoos. About 90% of the area is drained by the Colorado River and its main tributaries include the Green, San Juan, and Little Colorado Rivers. The landscape is made up of high desert with scattered areas of forests. Many of the areas on the plateau are considered protected and have much cultural significance. This region has the highest amount of parklands in North America which include national parks, monuments, wilderness areas, and forests.

RAINBOW BRIDGE
RAINBOW BRIDGE

Rainbow Bridge in Utah is one of the world’s largest known natural bridges. It was discovered by non-Native Americans in 1909, by two expedition parties, lead by Byron Cummings and W.B. Douglass. Later, in 1910, President William Howard Taft proclaimed Rainbow Bridge a national monument. The Native-Americans have known about its exisence for centuries, it is considered a sacred spot by those tribes who in habited the area. The Paiute and Navajo tribes named the bridge Nonnezoshe which means “rainbow turned to stone.”

But, Rainbow Bridge was formed millions of years previous to these events. Rainbow bridge is made of sandstone, the base is a formation of Kayenta sandstone and the bridge is a softer Navajo sandstone. Kayenta sandstone is the reddish sands and muds laid down by inland waters and moved by winds over 200 million years ago. Navajo sandstone, created by waves of sand dunes deposited over an extremely dry period, happened less than 199 million years ago. These processes lasted millions of years. The dunes then dropped to depths up to a 1000 feet. Over the next 100 million years, both of these formations were buried by an additional layers 5000 feet deep, the pressure exerted from these layers of material consolidated and hardened the rock. Water then formed the rest. The water of Bridge Creek flowed from Navajo Mountain toward the Colorado River. Water in contact with sandstone dissolves the calcium carbonate, which cements together the grains. The stream flowed in a tight curve around a thin fin of soft sandstone that jutted into the canyon. The force of the stream eventually cut a hole through the fin, which then altered the course and flowed directly through the opening and enlarging it. Over time this sandstone arch was formed. The uplift of the Colorado plateau then occurred, causing river gradients to get steeper, especially the Colorado River, which created the bridge that exists today. The span of Rainbow bridge is reported to be 290 feet in height and 275 feet across. The top of the arch is 42 feet thick and 33 feet wide.

If you are in the southwest close to the Utah and Arizona border, you should check this place out. Do some research and plan ahead. We took a two hour boat ride from Arizona on Lake Powell and then a half mile walk to reach this natural bridge.

LAKE POWELL
LAKE POWELL
LAKE POWELL
LAKE POWELL

 

The difference between an arch and a bridge… A natural arch is a rock exposure that has a hole completley through it, formed by THE NATURAL SELECTIVE REMOVAL OF ROCK, while leaving the frame of the arch intact. A natural bridge is a type of natural arch, but WATER SOURCES CREATED AN OPENING, then flowed through it. Arches are more common than bridges.

2 thoughts on “COLORADO PLATEAU AND A SANDSTONE RAINBOW

  1. This is a fascinating article…I would like to re-blog it or create a hard copy – there is so much to study and so many astonishing structures that so far my research hasn’t gotten to geology. You write clearly and without language that is daunting!

    Liked by 1 person

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