Maybe your Dog got a little close while releaving himself?

 

it is salt from the roads.i get this question all the time at work.

 

I appreciate all the suggestions and theories. Since my original post it has not reappeared, so it would seem that the problem has gone away. Based on all of the theories, I have deduced that it is one of two things: (1) melted salt, or (2) rabbit pee (I saw bunny tracks and a few bunny turds under the car this morning...no pee, but where there's smoke there's fire)

Thank you all.

Class dismissed.