Dust is as much a part of the Wild West as guns, whiskey and cowboys. Churned up by the hoofs of millions of longhorn cattle and filling the streets of flyblown towns, it is the backdrop for many a shoot-out. Until recently, most assumed that the American West was a natural dust bowl where every cowboy breathed true grit. Now it seems that the dust was mostly man-made and came with the cows. Head 鈥檈m up, move 鈥檈m out 鈥� and choke on the dust. Before the cows and the cattle trails immortalised in TV series such as Rawhide, there was no dust. Even today, with Rawhide replaced by Brokeback Mountain in cultural iconography, the dust continues to permeate. It could even explain some of the changes in the region now blamed on global warming.
EVER since settlers moved west across the US there has been dust 鈥� clouds of it everywhere. It was part of the landscape, or so it seemed. But there were no records of the landscape of the West until the settlers arrived. Now evidence is starting to emerge which suggests that before the settlers there was very little dust.
The evidence comes from the San Juan mountains of south-west Colorado, downwind of the badlands of Arizona and New Mexico. There Jason Neff, a geochemist from the University of Colorado, Boulder, has been analysing sediments laid down over the past 5000 years in alpine lakes. Atmospheric dust was minimal throughout those five millennia until the mid-19th century, he says. 鈥淭hen bang. It was like flipping a switch. From about 1860 to 1900, dust deposition rates shot up.鈥� After flatlining for thousands of years, dust levels in the lakes rose fivefold and stayed there, only subsiding a little towards the middle of the 20th century.
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鈥淎fter flatlining for thousands of years, dust levels rose fivefold鈥�
This is surprising. Usually dry means dusty, and the American West has almost always been dry 鈥� often drier than today. There was a near permanent drought between 900 and 1300, during the era known globally as the Medieval Warm Period. That drought was so intense that it destroyed a series of long-lasting native American civilisations, including the Anasazi, whose cliff homes are now US national treasures. Yet the evidence from the San Juan lakes is that it was not dusty. Even as their civilisation was collapsing, the Anasazi seem to have protected their soils from erosion.
The European settler was different. After the close of the American civil war, as settlers began to head west in large numbers, dust started appearing in the lakes of San Juan. The settlers didn鈥檛 move into a dusty world, they created it. Or rather, it seems that their cows did. The settlers were moving into a landscape remarkably ill-equipped to cope with grazing animals, says Neff. 鈥淯nlike most other parts of the US, there were few grazers in the American Southwest until the white man came. No bison and few antelope or deer.鈥�
In the Great Plains to the east and north, bison roamed in vast herds. Their regular grazing had created tough grass, while the herds manured the soil. In the Southwest, the land had few defences against a sudden invasion of millions of livestock, whose teeth stripped the grass and whose hoofs punctured the hard crust of desert soils that protected them from the wind.
And the invasion was sudden. William Abruzzi, a historian of the American West from Muhlenberg College in Allentown, Pennsylvania, has charted how the huge herds of cattle streamed west, funded by a bubble of speculative investment, much of it from Britain. The ending of slavery in the US in 1865 meant nobody wanted to put money into the plantations. So the money went west, into railroads and herds of cattle and sheep that rode the rails to the wide open pastures beyond the Mississippi. By 1900, when sedimentation rates in Neff鈥檚 lakes peaked, there were 20 million cattle and 25 million sheep in the West, on public land or land bought for virtually nothing.
One of the biggest ranches was owned by the Boston-based Aztec Land and Cattle Company. In 1884, it bought a million acres of Arizona pasture from the Atlantic and Pacific Railroad Company, which had been given the land by Congress as an inducement to build a railroad to San Francisco. Aztec鈥檚 longhorn cattle came by rail from Texas, along with hundreds of cowboys.
The cowboys were instantly notorious. On the streets of Holbrook, a town of 250 people that was the company鈥檚 Arizona headquarters, they shot 26 people dead in 1886 alone. The local saloon was renamed The Bucket of Blood. Yet at the same time as the legend of the lawless American cowboy was being forged, an environmental tragedy was under way. And it was the cows rather than the cowboys that did the most lasting damage.
Like human life, land was dirt cheap in the Wild West. Aztec paid just 50 cents an acre for a ranch the size of Delaware. Speculators were only interested in quick profits and had little incentive to protect the soils from overgrazing. By the time Aztec sold the ranch in 1901, it was barren, with cattle carcasses scattered across the exhausted land.
鈥淒uring its brief reign the Aztec company had a devastating impact,鈥� says Abruzzi. Waist-high grasslands that had covered the hills and plains of Arizona in the early 1880s were eaten up in little more than a decade. Such was the damage that even now few of the pastures have recovered. The parched and exposed soil simply blew away.
The mythologising of the West in 20th-century cowboy movies and TV series such as Rawhide has rather obscured the fact that the ranchers were much hated in their time. They occupied land theoretically earmarked by the 1862 Homestead Act for settlers. Under this law, aimed at populating the West, any family willing to make the arduous journey was entitled to claim 160 acres and farm it. Yet by the time people moved west in large numbers, the cattle companies had taken most of the land, surrounded it with barbed wire, commandeered the water sources and were repulsing all comers by force of arms.
Some scientists at the time were aware of the damage the ranchers were doing to the land. In 1894, naturalist John Muir called the great livestock herds 鈥渉oofed locusts鈥� carrying desolation with them鈥�. The pioneering American plant ecologist Frederic Clements argued 鈥渢hat the white man鈥� came as disrupter, an alien and exploiter鈥�.
Soil scientists have known for a while about the importance of the hard crust that forms on arid soils, and how vulnerable it is to hoofs. 鈥淭hese crusts can survive wind speeds of a hundred miles an hour, but cattle break the crust,鈥� says Jayne Belnap, a soil ecologist at the US Geological Survey in Moab, Utah. 鈥淒eserts are usually not dusty at all until you break the crust.鈥�
The scale of the dust clouds created by the livestock invasion has until now been largely unknown. When Neff began finding dust in Colorado lake sediments laid down in the 19th century, he was initially unsure where it came from. Maybe it had crossed the Pacific from China鈥檚 notoriously dusty Gobi desert. But analysis of the size and chemical composition of the dust tied most of it to the American Southwest, mainly Arizona and New Mexico.
It was only in the 1930s, with the passage of the Taylor Grazing Act, that federal authorities sought to rein in the herds. Numbers are much reduced today. But with the soil crust gone, dust clouds still head north, occasionally sprinkling the ski slopes of Colorado. In the lakes, Neff says, deposition rates are still between three and four times pre-19th-century levels ()
The dust is having significant ecological effects in the Colorado mountains, bringing nutrients into alpine ecosystems normally shaped by nutrient shortage. But perhaps the most dramatic impact of the dust has been on snowfields in the Rockies. Even a thin sprinkling of dark material makes snow and ice absorb more solar radiation. That means a faster spring snowmelt. Neff鈥檚 colleague Tom Painter of the University of Colorado鈥檚 National Snow and Ice Data Center reported last year that by more than a month.
The loss of snow and the shrinking of many glaciers across the American West in the past century is frequently blamed on global warming. In Montana, for example, cover since it was made a park in 1910, a fact almost universally attributed to warmer temperatures. Warming almost certainly plays a role, but Painter and Neff鈥檚 findings suggest that dust may also contribute. Painter is heading there this spring to take samples of snow and dust to test the idea.
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