Interesting Look to #1 Fwy

I don't know for sure what the cause of this is, but there are distinct lines of different looking turf on both sides of the first fairway.  It's possible that at some time, the sides of the fairway were killed off and seeded with a different variety of bentgrass, but there is also defined lines of earthworm activity.  The earthworm activity leads me to believe that there is some difference in the soil on the outsides of the fairway. 

The black specks in the grass on the left side of the picture are soil castings, created by earthworms.