Over the last few years, a few storms have brought a thin layer of red snow to the Rockies and front range. I can remember a storm of an inch or two leaving my car covered in a film of red dust after the snow melted.
Apparently, the dark-colored fine sand catches heat from the sun and melts the snow much faster.
Scientists say the dust is caused by farming and grazing in the southwest. Nodoubt part of it, but the Southwest seems to produce plenty of fine red dust without our help. It could be that this has been going on at some level for thousands or millions of years.