I was thinking that this stuff was originating inside the engine via a PCV / breather line. Note how concentrated it is in a very small area. I agree that the shape of the pattern has to do with the swirl in the box. Like I said earlier, I've never seen an air filter like this before, particularly one this dirty with so few miles. This vehicle was stuck for hours in a snow storm last November, breathing in the exhaust of other cars. Somehow I doubt that this has anything to do with it. Perhaps I will check it in a few months at the next oil change and see if there is a similar pattern.