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Images of deserts in the United States show dusty, barren landscapes, but the land may not always have been this way. Ever since settlers moved west across the US, there has been dust, clouds of it, everywhere. It was part of the landscape, or so it seemed to them. 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 southwest Colorado, downwind of Arizona and New Mexico. There, Jason Neff, a geochemist from the University of Colorado, has been analyzing sediments, the sand, stones and mud, laid down over the past 5,000 years. Atmospheric dust was minimal throughout those five millennia until the mid-19th century, he says, but then, ‘from about 1860 to 1900, dust deposition rates shot up.’
This is surprising because usually dry means dusty, and the American West has almost always been dry, often drier than today. There was a near-permanent drought between 900 and 1300 which was so intense that it destroyed a series of Native American civilizations, 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 civilization was collapsing, the Anasazi seem to have protected their soils from erosion.
