I was shocked at the amount of sand and mud that my bike had collected on a mere three-hour ride yesterday. Though I was cursing the rain at the time, I was mildly comforted by the knowledge that it was washing away all of the bicycle-eating salt from the roadways.
The rain ended mid-ride, which allowed all of the sand to accumulate (as pictured below). The bike was clean at the beginning of the ride.
Welcome to mud season.