Call the City of Cotati police department immediately! Try to get a good description of the person dumping, the vehicle that they were driving, and the vehicle license number. If you see illegally dumped trash after the fact and cannot provide a description of the responsible party, where the trash is located will determine how it is to be removed.
If the debris is located on the public property i.e.: street, sidewalk, alley, or other City-owned property, call Public Works Department at 707-665-3638.
For dumping on a vacant lot or private property, call the Building Department at 707-665-3636.