Rock Chip from...

I am so angry right now.  I left work not happy but ok because I have to figure out a problem that a parent just threw out to me, that's not why I'm angry.  I'm angry because to add to that I had this happen:

I felt the impact and I was only going 45 mph at the time.  I didn't see where it came from so I'm blaming it on a rock.  There was someone hauling a trailer full of wood/scraps/something in front of me and he didn't have it covered so something could have flown out, but I didn't see it as it's on the passenger side almost behind the rearview mirror.  I'm blaming it on a rock because I figure it's better than blaming a person especially falsely blaming a person.  I don't know if you can tell from the picture or not, but the circle is about the size of a baseball and the point of impact is in the very center but with nothing coming off of it.  I am so mad.