Arches National Park in eastern Utah, USA has the greatest concentration of natural rock arches anywhere in the world (see map).  The arches in the area are developed in reddish quartzose sandstones of the Slick Rock Member of the Entrada Sandstone (Jurassic).


The geologic origin of the arches is a moderately complex story (partial dissolution of salt diapirs, collapse & differential erosion of overlying jointed sedimentary units, development of long & moderately tall sandstone ridges, surficial undercutting along the base of the Slick Rock Member, gaps form along the sandstone ridges).




This is the South Window Arch, located in the Windows section of Arches National Park.


South Window Arch is located at the southern end of the ridge near center. (Satellite photo provided by DigitalGlobe & Google Earth)



The opening scenes of the Steven Spielberg movie Indiana Jones and the Last Crusade were filmed in the Windows section of Arches NP, particularly in the Balanced Rock & Double Arch area.




Balanced Rock in Arches National Park.  The Balanced Rock itself is relatively hard quartzose sandstone (Entrada Sandstone, Slick Rock Member).  The underlying beds are softer interbedded fine-grained & coarse-grained siliciclastics (Entrada Sandstone, Dewey Bridge Member).  The Dewey Bridge unit, being softer, weathers & erodes more quickly.  The Slick Rock unit, being harder, erodes more slowly.



Balanced Rock is the shadowed patch of red rocks at center. (Satellite photo provided by DigitalGlobe & Google Earth)



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