What is all this brown stuff on the roads?

Got out on my 20 mile back road loop today. I think this was one of first rides this year where I saw more dirt on the road than snow and ice. There were both today and even mud. Not so happy about that, now I have to clean the bike. I was surprised it was as muddy as it was since the temps were in upper teens when I left the house. The new bike felt great. I swapped around the spacers under the stem and think I have found a really comfortable set up with the flat bar. There are a few minor things I need to take care of though. My back up wheelset, the spokes keeping coming un-done, that is they are coming unscrewed. I had the wheel tensioned and 2 rides later the stupid spokes are loose again. I guess I am either going to have to loctite them on, or get some different spokes. But it is a good time of year to work all the bugs out. Getting the bike up to speed it just flies and seems to float over bumps. I cant wait to get it out on some trails. Hopefully only another month of this stupid winter stuff to go.