The barren rockscape of south-eastern Utah resembles the surface of some fantastic planet. Rugged pillars of rock, sculpted to every imaginable shape and size, just up from the desert floor. But far more astonishing are the 200 or so stone arches that span openings in walls of rocks and give the area its name. Landscape Arch is the world’s longest natural arch – a ribbon of stone, barely 6ft (1.8m) thick at one point, stretches 291ft (89m) between massive buttresses.
The eye of the Whale is an elongated slit beneath a huge span of rock. The most distinctive arch, however, is the freestanding Delicate Arch. Shaped something like an inverted ‘U’ with splayed sides, it stands on the rim of a great natural amphitheatre.
Equally evocative names have been given to other landforms of Arches, which is one of the United states’ national parks. Some bear a freakish likeness to humans, objects or animals. The Dark Angel, a pinnacle of black rock 125ft (38m) high, presides over an area known as the Devil’s Gardens, and the Tower of Babel is a soaring 500ft (150m) slab of ribbed rock.
The rock formations of Arches are carved out of sandstone – grains of quartz held together by a cement of silica or calcium carbonate and coated with iron compounds that give the rock its many colours. The sandstone of the Arches area lies on top of a thick layer of salt. Under pressure from the overlying rock, the salt can move into weaker areas in the rock and itself apply pressure to those weaknesses.
In the Arches area, moving salt has forced the sandstone upwards into the dome, stretching and cracking it and resulting in hundreds of parallel joints 10-20ft (3-6m) apart. Water seeped into the joints, and the rock of the intervening fins was easily weathered more in their lower layers until the rock broke through to leave an arch.
Normally, arches take shape imperceptibly slowly, but occasionally there is a dramatic change, such as the one at Skyline Arch in 1940. The arch was known as ‘Arch in the Making’ until a gigantic slab of sandstone tumbled from the opening, doubling its size.
This part of Utah is known as ‘red rock country, but almost every hue is present in this semi-desert where little vegetation obscures the rocks. Some of the rock forms are draped with ‘desert varnish’ – a coating of minerals left behind as seepage water evaporates. The Ute people etched drawings of men on horseback into the varnish, sometime after horses, brought to America by the Spaniards, had reached this area during the 17th century.
The climate of Arches is harsh. Less than 10m (250mm) of rain falls each other, and the temperature, which drops below freezing in winter, can rise to 38C (100F) or more in summer, with the rock a searing 66C (150F). Yet ferns and orchids flourish in cool overhangs and moist alcoves.
Most animals in the area rarely emerge during the day, but after nightfall, the desert comes to life, as animals including bobcats and long-eared mule deer hunt or forage amid the monstrous shadows of the moonlit rocks.