The Northwest Mud Flaps is a factory in Gravity Falls, Oregon that produces mudflaps. The factory releases toxic waste that pollutes the adjacent river, and drinking the water leads to mutations on the nearby wildlife and animals of the nearby Petting Zoo, including Octavia. Judging by the name, it can be presumed that it is owned by the Northwests.
Preston Northwest owned the factory when he met the soon-to-be Priscilla Northwest. Sprott explains that he found the mutated, eight-legged cow Octavia near there. The factory produces a toxic chemical that causes animals who drink it to grow extra parts on their body and supernatural powers.
The factory is brown with two chimney stacks and a waste pipe along the side of the building, with the sign Northwest Mud Flaps, the factory name. It has several windows along the sides.