Ever since European settlement of the West, there has been dust, caused by outside forces breaking the fragile crust that holds undisturbed desert soil in place. Initially, grazing cattle kicked up the dust. Scientists say it is now more likely to be caused by off-road vehicles, mountain bikers or energy exploration. In a study last year, Neff found that the amount of dust in the Rockies is five times greater than before the late 19th century.
"This is really the story of the wholesale transformation of the West," Painter said.
… (S)ome scientists note that the West has ended an unusual, 50-year wet period and is returning to its normal, more arid state.