Federal authorities in southern Arizona say they have shut down one of the longest drug tunnels ever discovered in the border city of Nogales. A task force led by U.S. Immigration and Customs Enforcement's Homeland Security Investigations also arrested three men late Monday and seized more than 640 pounds of marijuana and a half-pound of heroin. Authorities say the 481-foot tunnel runs between two private residences accessed by shafts at each end. The tunnel stretches 411-feet from the U.S. entrance to the international border and extends for another 70-feet into Mexico. The passageway is about two-feet wide by three-feet tall and contains wood shoring, electric lighting and fans to circulate air inside. Two of the arrested men are from Mexico while the other is from Nogales.