Arches National Park is a U.S. national park in eastern Utah. It is known for preserving over 2,000 natural sandstone arches, including the world-famous Delicate Arch, in addition to a variety of unique geological resources and formations.

The park is located near Moab, Utah, and is 119 square miles (310 km2) in size. Its highest elevation is 5,653 feet (1,723 m) at Elephant Butte, and its lowest elevation is 4,085 feet (1,245 m) at the visitor center. Since 1970, forty-three arches have toppled because of erosion. The park receives 10 inches (250 mm) of rain a year on average.

The area, administered by the National Park Service, was originally designated as a national monument on April 12, 1929. It was redesignated a national park on November 12, 1971. More than 833,000 people visited in 2006.

Features

Among the notable features of the park are:

* Delicate Arch — a lone-standing arch which has become a symbol of Utah

* Balanced Rock — a large balancing rock, the size of three school buses

* Double Arch — two arches that share a common end

* Landscape Arch — a very thin, very long arch over 300 feet (100 m); the largest in the park

* Fiery Furnace — an area of maze-like narrow passages and tall rock columns (see biblical reference Fiery Furnace)

* Devil's Garden — with many arches and columns scattered along a ridge

* Dark Angel — a free-standing column of dark stone at the end of the Devil's Garden trail

* Courthouse Towers — a collection of tall stone columns

* Petrified dunes — petrified remnants of sand dunes blown from the ancient lakes that covered the area.

* Wall Arch —located along the popular Devils Garden Trail. Collapsed sometime on August 4-5, 2008

Geology

The national park lies atop an underground salt bed, which is the main cause of the formation of the arches and spires, balanced rocks, sandstone fins, and eroded monoliths in the area. Thousands of feet thick in places, this salt bed was deposited over the Colorado Plateau some 300 million years ago when a sea flowed into the region and eventually evaporated. Over millions of years, the salt bed was covered with residue from floods and winds and the oceans that came in intervals. Much of this debris was compressed into rock. At one time this overlying earth may have been one mile (1.6 km) thick.

Salt under pressure is unstable, and the salt bed below Arches was no match for the weight of this thick cover of rock. Under such pressure it shifted, buckled, liquefied, and repositioned itself, thrusting the Earth layers upward into domes. Whole sections fell into cavities. In places they turned almost on edge. Faults occurred. The result of one such 2,500-foot (760 m) displacement, the Moab Fault, is seen from the visitor center.

As this subsurface movement of salt shaped the Earth, surface erosion stripped away the younger rock layers. Except for isolated remnants, the major formations visible in the park today are the salmon-colored Entrada Sandstone, in which most of the arches form, and the buff-colored Navajo Sandstone. These are visible in layer cake fashion throughout most of the park. Over time water seeped into the superficial cracks, joints, and folds of these layers. Ice formed in the fissures, expanding and putting pressure on surrounding rock, breaking off bits and pieces. Winds later cleaned out the loose particles. A series of free-standing fins remained. Wind and water attacked these fins until, in some, the cementing material gave way and chunks of rock tumbled out. Many damaged fins collapsed. Others, with the right degree of hardness and balance, survived despite their missing sections. These became the famous arches.

credited to wikipedia and flickr: Bill Wight CA