Have you confirmed that these are gophers and not moles? Their dirt mounds can be confused. In either case, no, their is nothing that is legal to spread on the surface to kill them. You would need to either bait directly into the active runs or set body-gripping (killing) traps in the active parts of the run. Trap design and placement however, differ by those two species. 
Fresh molehills will have a "volcano" shape with a slight plug in the middle, whereas a fresh gopher mound will be more fan-shaped, sloping, and have a plug to one side.