I have some friends in the West and they claim it covers the entire area during Early Spring...

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As you probably know, the yellow-green dust covering everything that doesn’t move this time every year is pine pollen. Pine trees produce large (very large) amounts of pollen each spring in order to ensure that the seeds get fertilized and the species can survive. You may not know this, but pine trees have both male and female pine cones. The male cones are usually smaller and often not even noticed, but the pollen that they produce is. So, if your car is yellow, blame a male.

Now, if your seasonal allergies are kicking up with all of this yellow-greenish pine pollen, don’t blame a pine tree. Most people think that the pollen they see is the culprit causing their sneezing, but other male agents are at work here. Pine pollen is large and heavy and drops quickly to the ground, which is why it coats everything. But, because it drops out of the air quickly and also because it has a waxy coating, it usually isn’t a cause of allergies. The main cause of your sneezing is all of the other trees that are producing pollen at the same time. Oak tree's for one.

http://www.crossville-chronicle.com/news/glade_sun/is-your-car-covered-in-yellow-dust-blaming-it-on/article_86d24955-370f-54c9-9343-9a2d8dad02ce.html