The west wasn't always so dusty. It got a whole more so in the past 200 years, 500 percent more so—thanks to American expansion, complete with trains, ranches, and livestock. Sediment records from dust blown into alpine lakes in southwest Colorado's San Juan Mountains over millennia indicate the sharp rise in dust deposits beginning in the middle of the last century. "From about 1860 to 1900, the dust deposition rates shot up so high that we initially thought there was a mistake in our data," said geologist Jason Neff of the University of Colorado Boulder. "But the evidence clearly shows the western U.S. had its own Dust Bowl beginning in the 1800s when the railroads went in and cattle and sheep were introduced into the rangelands. There were an estimated 40 million head of livestock on the western rangeland during the turn of the century, causing a massive and systematic degradation of the ecosystems." The 1934 Taylor Grazing Act imposed restrictions on western grazing lands, and the deposits show a coinciding decrease in dust that continues to this day.
Another reason to bring back the bison.