Erosion has transformed the Badlands of South Dakota into a landscape like no other on Earth.
Steep ridges are broken up by deep ravines, their tinted, horizontal bands notched with dozens of vertical channels. Narrow, flat-topped hills tower high into the air, in places capped by a jumble of rocks and boulders.
Formation of the Badlands
Around 80 million years ago, the region now occupied by South Dakota's Badlands was a shallow sea. Its bed was full of rich and varied sediments.
About 65 million years ago, the same upheaval in the Earth's crust that formed the Rocky Mountains crumpled this seabed, pushing it upward. The land was transformed from an immense, marshy plain into a rolling prairie covered in rich green grass and patches of coniferous forest.
Erosion
Wind, freezing temperatures and running water have transformed what was once a rich pastureland into a decaying landscape.
Torrential rains that fall in spring and early summer both shape and erode the semi-arid Badlands.
Only 38cm (15in) of rain falls each year, but most of it arrives in intermittent downpours of tremendous violence.
The Badlands become a network of gushing streams and powerful rivers. Water cascades from ridges and rushes through ravines with astonishing force.
Because the ancient, soft sedimentary layers have never been compressed by harder rock, they are invaded and washed away by running water.
The runoff joins the White River and then the Missouri, taking with it a huge cargo of clay, stones and gravel.
Devoid of vegetation, the rocks of many hills crumble at the slightest touch. Nearly every footfall loosens stone fragments, which tumble down into the ravines. Pinnacles of rock, such as Vampire Peak, are being reduced in height by as much as 15cm (6in) every year.
Fossils
The sedimentary rocks contain fossils that show the variety of animal life that inhabited the region as it metamorphosized from sea to fertile plains.
Marine turtle shells are one of the most common fossils found in the Badlands - the largest was 3.7m (12ft) long.
Fossils of oreodonts are also common. These mammals resembled pigs. They had large teeth that were probably used for ruminating.
The largest animal was probably Brontotherium, a four-legged herbivore that stood over 2.5m (8ft) tall at the shoulder. On the snout of its tiny head was a long, thin horn of solid bone bisected at the tip into two branches.
Less than half this size was Mesohippus, a small, three-toed ancestor of the modern horse.
Life in the Badlands
It is difficult for living creatures to maintain a permanent residence in the Badlands
A site that has provided a niche for a generation may disappear overnight.
However, there are sheltered pockets where animals, such as the prairie dog, and plants, like buffalo grass and the prairie golden pea can live successfully. Most of these pockets are on the fringes of the Badlands where the soil is more stable.
Prairie Dogs
Prairie dogs are burrowing rodents that live in underground colonies or "towns". These towns are made up of highly ordered networks of tunnels and chambers. They have designated areas for storing food, sleeping and defecating.
The black-footed ferret is one of the prairie dog's predators
The White River
The White River's name comes from the Badlands' chalky sediments, which do not settle but remain permanently in solution.
The Wall, a desolate stretch of cliffs and buttresses around 60m (200ft) high, is the main source of chalk.
The only creatures that can survive on The Wall are bats, rodents, such as the Badlands chipmunk, and reptiles, including bull snakes and rattlesnakes.