Illegal yard debris dumping

Yesterday afternoon someone pulled into our driveway and pulled out quickly. This morning we found a truck load of yard debris--fir branches, scotch broom, weeds--piled in the middle of our driveway blocking passage. It required a bit of time to clear it. This is not only a nuisance, but a hazard, in that it would have blocked fire or emergency vehicles. Does anyone know of similar occurences? Or has anyone spotted a suspicious looking truck filled with yard debris?

John Christensen
(503) 695-2474