The first time it happened, the dirt came all the way from Mongolia. There were more questions Thursday about where the muck came from.
9NEWS spoke to one dust expert who says it takes just the right mix for dust to stick to your car.
Wednesday night, the ingredients lined up. A wind storm coming from the western desert carried the dust across the mountains.
Once the right amount of moisture was added, the result was muddy cars.
University of Colorado Geology Professor Jason Neff says the dust blew in from a wind storm in Northern Arizona. When you add moisture to that dust, it forms a clay-like glue to your car.
"The winds roll across the desert, and the dust gets picked up and sort of surfs along right behind that storm. When it rains or snows, then that dust falls out of the atmosphere on to your windshield," Neff said.
9NEWS received several news tips asking if this dust was possibly ash from the Iceland volcano.
Neff says dust typically does not travel that far of a distance.
"It would have to have wrapped all the way around the world basically, and come all the way to Colorado," he said.
Although dust experts say this maybe a hassle to clean up, a lot of Colorado's richest soils actually have their origin in dust.
"It's not such a good thing for the deserts, but for us in Colorado, it actually fertilizes our soils a little bit," he said.
Several car washes told 9NEWS they noticed an increase in customers. Neff says if you want to clean off your car, it is best not to scrub the car. Some of the soil particles are abrasive and they can scratch off the paint.
Instead, he suggests you take a hose to your car.
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